Genetics Box

This box hooks students into the study of genetics by investigating the inheritance of human traits. Drawn by students' natural curiosity about how they come to look the way they ...

This box hooks students into the study of genetics by investigating the inheritance of human traits. Drawn by students' natural curiosity about how they come to look the way they do, they learn the basics of Mendelian genetics. From this introduction, students extract DNA, build DNA models and use them to study replication, transcription and translation. The DNA activities culminate in a CSI investigation in which students must solve a mystery using DNA fingerprinting. The unit then zooms back out from the molecular level to look at natural selection and the evolution of species. A version of the classic bird beak buffet activity is provided as well a wide variety of extensions to delve into evolution in greater detail.

1. Human Traits

Summary
Genes and DNA are very abstract concepts for students. In order to "hook" them in, I open my genetics and evolution unit with human genetics, specifically looking at the variations in human traits. This allows students' natural curiosity about their identity to draw them into the study of heredity. There are lots of great single gene traits with simple dominance inheritance patterns to explore: earlobe attachment, tongue rolling, cleft chin, etc. There are some polygenic traits that can be explored: hair color, eye color, reach, reaction time, etc. Hair texture (curly, wavy, vs. straight) offers a good example of incomplete dominance. After collecting information from themselves and two others, the population data is collected on several large charts in order to look for and discuss the patterns.

Objectives
Can describe human traits.
Can distinguish between single gene and polygenic traits.
Can use tables to organize data and create histograms to graphically represent data.
Can identify patterns in data and draw conclusions from those patterns.

Vocabulary
Characteristic
Trait
Gene
Polygenic
Histogram

AttachmentSize
1traits_survey.doc56.5 KB
traits_handout.doc624.5 KB
traits_handout.pdf844.61 KB

1. Human Traits - Logistics

Time
Introduction - 30 min
Collect, organize and analyze data - 50 to 100 min depending on the depth of your analysis

Grouping
Small groups in class and at home for data collection. Whole class for the analysis of the collected data.

Materials

  • Copies of the "Human Traits Survey" handout
  • Rulers
  • Meter sticks or measuring tape
  • 6-8 large sheets of butcher paper or flip chart paper, preferably with gridlines for graphing
  • colored removable labeling dots

Setting
Classroom.

1. Human Traits - Background

Teacher Background
If you were asked to describe yourself to a stranger so they could recognize you at the airport, what would you say? What traits make you unique and different from others? The general ways one person can different from another – height, eye color, hair color, build, complexion, etc – are called characteristics. The precise description of an individual – 5’2”, brown eyes, brown hair, fairly thin, etc. – are called the person’s traits.

In this activity, students survey themselves and others that aren’t in the school for a wide array of traits. Some are “yes/no” traits – dimples/no dimples, freckles/no freckles, attached earlobes/unattached earlobes, etc. Others are “multiple choice” traits – blond/red/brown/black hair, blue/green/hazel/brown eyes, etc. Others vary even more widely – reaction time, hand span, reach, etc. In fact, most of these when plotted on a histogram will generate a bell curve.

These differences relate to the number of genes controlling that characteristic. Most simple “yes/no” traits are controlled by a single gene. Most “multiple choice” traits are controlled by a small number (2-4) genes. The widely varying traits are governed by a large number of genes.

In running this activity, it is essential to be sensitive to the different family situations your students may be in. In the past, it has been traditional to survey one’s immediate family for a series of traits and generate a family pedigree. However, with the number of divorced, adopted, single-parent, and same-sex families in our schools today, it becomes much more difficult to negotiate a unit on inheritance without hurting someone’s feelings. Therefore, my approach is to ask students to survey any two people from outside the school. If it is possible to survey your biological parents, great! If not, any two people from outside school is fine.

Student Prerequisites
None

1. Human Traits - Getting Ready

Getting Ready
Day 1 - Introduction

  1. Make copies of the "Human Traits Survey" handout.
  2. Set out rulers, meter sticks and/or measuring tape.

Day 2 - Collect and organize data

  1. Fill out the "Human Traits Survey" for yourself.
  2. Create 4 large graphs on which to draw histograms of the "Traits measured in centimeters" data. Students will be placing a sticker onto the chart for each person surveyed, eventually creating a bell curve distribution for each trait. The y axis for each trait should be labeled "Number of people".
    • Hand span - Label the x axis between 1-30 cm.
    • Reaction time - Label the x axis between 1-30 cm.
    • Reach - Label the x axis between 150-280 cm in 5 cm units.
    • Broad jump - Label the x axis between 80-220 cm in 10 cm units.
  3. Create a summary table on which to synthesize the population data for the "Yes or no/multiple choice traits". Students will put a tally mark beside the applicable trait for each person surveyed.
  4. Cut the sheets of sticky dots into smaller sheets with 12 dots per sheet. If you are using multi-colored dots, make sure there are 3 dots of each color per sheet.
  5. Write your name (or initials) on 4 dots. Plot those dots onto the histograms where your own data falls.
  6. Place a tally mark beside each of your traits on the summary table.

1. Human Traits - Lesson Plan

Lesson Plan
Day 1 - Introduction

  1. Pose the following scenario to your students: “An exchange student from England is coming to stay with your family for a month. You go to the airport to pick her up and need to describe yourself to her so that she can find you in the crowd at the airport. In 2-3 sentences, how would you describe yourself?” Solicit volunteers to describe themselves.
  2. After 5 or 6 students have shared, draw attention to some of the general categories of responses. Note how some descriptors are biologically based (eye color, ethnicity, hair color, height, etc.), whereas others are environmental (clothing, accessories, dyed hair, etc.). In this class, we will focus on the biological descriptors.
  3. Go over the vocabulary. “Characteristics” are the general category of descriptions (height, eye color, etc.) whereas “traits” are the precise description of an individual’s characteristics (5’2”, blue eyes, etc.).
  4. Pass out the human traits survey. Read the instructions together, then answer any questions about the survey.
  5. Allow students to work individually or in pairs to survey their traits.
  6. Completion of the survey for individuals not in your classes should take place as homework that evening.

Day 2 – Collect and organize data

  1. Give each student a sheet with 12 sticky dots.
  2. Have students write the name (or initials) of each person they surveyed on the dots. Each person surveyed should end up with 4 dots total. If using multi-colored dots, each person should have their name on a dot of each color.
  3. Describe to the students how a histogram is constructed with the range of possible traits on the x axis and the number of people in a given category on the y axis. Show students how to add their dots to the charts, making sure they understand how the dots stack one on top of the other.
  4. Describe to the students how to add a tally mark to the summary table beside the traits for themselves and the people they surveyed.
  5. Allow students time to add their information to the graphs and tables.
  6. If you have multiple classes, you may want to postpone the analysis and discussion part below until after all classes have added their information to the tables.

Day 3 – Analyze data

  1. This is the opportunity for your students to look at the tables and graphs and look for patterns the different kinds of traits. Before you begin, make sure students know how to find an average, median, range, outlier and percentage. Use a few examples to help them with the statistics.
  2. Either as a class or in small teams, summarize the data – you may wish to have students create a summary table, pie chart, histogram or other graph in their lab notebook. What was the average broad jump distance? What was the range? Were there any outliers? What percentage of people were blue eyed? What percentage had freckles?
  3. Look for patterns. Do the 4 histograms look the same in shape (they should all form a bell curve distribution)? What would histograms look like for the yes/no/multiple choice traits? What would the histograms look like for other traits that were not surveyed like height, age, favorite color, hair length, test scores, etc.?
  4. What is the source of all these differences between people (genes and environment)? Discuss the contribution of genetics (nature) versus environment (nurture). With broad jump distance as an example, how much is determined by genetics and how much is determined by environment like practice?
  5. From here, there are many different ways to take the discussion:
  • Discuss the difference between the traits measured in centimeters versus the yes/no/multiple choice traits. How many possible outcomes were there for traits measured in centimeters? If the yes/no/multiple choice traits were plotted on a histogram, what would the histogram look like? What is the biological difference between these 2 categories (traits measured in centimeters depend on many genes while yes/no/multiple choice traits depend on a small number of genes)?
  • Discuss the evolutionary advantage of different traits. Is there an advantage to having a broad hand span? Is there an advantage to having a small hand span?
  • Lead the discussion into a description of basic Mendelian genetics. For each of the yes/no traits, one trait is dominant and the other is recessive (see Making Babies lab for additional information). Eye color and hair color are more complicated because they are determined by multiple genes. Hair texture is more complicated because it is determined by codominance. Discuss how each person has 2 genes for each trait, one from mom and one from dad. The combination of these genes is what determines your traits.

1. Human Traits - Assessment

Assessment

  1. Collect Traits Survey forms.
  2. Collect lab notebooks with students’ summary tables and graphs.
  3. Give students a data set for a trait like height or SAT scores and ask them to generate a histogram independently.

Going Further

  1. Enter into a more serious discussion of Mendelian genetics and the allele combinations that determine various traits. See Making Babies lab for a one potential way to lead this discussion.
  2. Have students to compare one population to another. Are the adults surveyed different than the kids? Ask a nearby school (or different classroom within the same school) to conduct the same survey and compare your results. Another way to investigate this type of information is through the CIESE Collaborative Project. They have compiled a very large database of population genetic information from schools around the world concerning the following traits: earlobe attachment, white forelock, dimples, hitchhikers thumb, bent pinkie, mid digit hair. Their database may be downloaded in Excel format from their website.

1. Human Traits - Sources and Standards

Sources
The idea for this activity was inspired by Katie Ward, a superwoman science teacher from Aragon High School. Another traits survey activity for the classroom with a slightly different twist can be found through the NASA Explores website.

Any resource list I might compile would be incomplete next to the genetics resource list created by 42Explore.


Standards

Grade 7
Genetics
2. A typical cell of any organism contains genetic instructions that specify its traits. Those traits may be modified by environmental influences. As a basis for understanding this concept:
c. Students know an inherited trait can be determined by one or more genes.
d. Students know plant and animal cells contain many thousands of different genes and typically have two copies of every gene. The two copies (or alleles) of the gene may or may not be identical, and one may be dominant in determining the phenotype while the other is recessive.

2. Making Babies

Summary
This is an extension of the Human Traits survey activity designed to introduce students to genes, genotypes, and simple inheritance patterns. Using information from the Human Traits Survey, students make guesses about their own genotype, create gametes from their genotypes, then make “babies” with a partner. Along the way students discover answers to the questions: What are genes? How are genes (and traits) passed on? How are gametes different than other cells in our body? Why do I look like mom in some ways and dad in other ways and neither of them in still other ways? Why don’t siblings look alike?

Objectives
Can explain the relationship between genotype and phenotype.
Can explain the inheritance of single gene traits using dominant/recessive relationships.
Can take genotype information from 2 parents, model the creation of gametes by independent assortment, and use those gametes to create offspring.

Vocabulary
Trait
Phenotype
Genotype
Gene
Allele
Dominant
Recessive
Incomplete dominance
Homozygous
Heterozygous
Gamete
Zygote

AttachmentSize
babies_handout.doc60.5 KB
2making_babies.doc61 KB

2. Making Babies - Logistics

Time
50 minutes

Grouping
Individual initially then later in pairs. The teacher should devise a way to break the students into pairs (ramdomly or assign beforehand). Allowing students to pick their own partners is NOT a good idea for this activity. It is not necessary to have mixed gender pairs. In fact, the same gender pairs tended to be more mature about the whole thing.

Materials

  • Completed “Human Traits Surveys” (download from the bottom of the Human Trait lesson)
  • Copies of the “Making Babies” handout
  • Pennies
  • Colored pencils

Setting
Classroom

2. Making Babies - Background

Teacher Background
One of the greatest mysteries – how we inherit traits from our parents – was solved in the 1800s by the Austrian monk Gregor Mendel. Although he published his work in 1866, it went almost entirely unrecognized until the 1900s, long after his death.

Mendel worked with pea plants, carefully characterizing their traits and cross-breeding them over many generations. He observed that many traits occur in only two different forms (short or long stems, purple or white flowers, round or wrinkled seeds). When a short plant is crossed with a tall plant, the offspring are all either tall or short, not of middle stem length. This observation countered the “blending theory” that was generally accepted at the time.

Mendels peasMendels peasHe established many pure-breeding lines – for instance short plants that when cross-bred always had short offspring and tall plants that always had tall offspring. Interestingly, when a pure-bred short plant is crossed with a pure-bred tall plant, the first offspring (f1 generation) are all tall! If these tall f1 plants are cross-bred to one another, the next generation (f2) consistently have a 3:1 ratio of tall to short plants.

With these ratios and careful breeding experiments, Mendel discovered the basic laws of inheritance. He came to several conclusions:

  1. That traits are determined by “factors” (now called genes) that are passed from parent to offspring in an unchanged, undiluted, unblended form.
  2. Everyone has 2 copies of a “factor” for each trait, one from each parent.
  3. Even if a “factor” does not show up physically in an individual, that “factor” can still be passed on to the next generation.

Thus, what happened in Mendel’s tall x short plant experiment was this… The pure breeding tall plant can be represented by TT. The pure breeding short plant can be represented by tt. Each letter (T or t) represents one factor or gene. Since each individual has 2 copies of every factor or gene, each plant has 2 letters to represent its combination of genes (its genotype). The different forms of the gene (alleles) are represented by capital versus lower case letters.

When the tall and short plants were crossed, each parent gave the offspring one of its two genes. The result is that all the offspring inherit the combination Tt. All of these f1 plants are tall. Thus, the tall T allele covers up the short t allele resulting in tall f1 offspring. The tall T allele is therefore said to be dominant over the short t allele and the short t allele is recessive to the tall T allele.

These tall f1 plants with the genotype Tt are then crossed to one another. Since the offspring can be given a tall T allele or a short t allele, there are 4 possible combinations that may occur, each are equally likely: TT, Tt, tT or tt. Only tt would produce a short plant since in all the other cases, the dominant tall T allele is present to cover up any recessive short t alleles that might be present. Thus, there is a 3:1 ratio of tall to short plants in this f2 generation.

This can be graphically shown in what is known as a Punnett square which resembles a multiplication table as shown at left.

This inheritance pattern is simplest of all possibilities. It gets a whole lot more complex when you consider incomplete dominance (where the heterozygotes that have two different alleles like Tt have an intermediate phenotype), X linkage (what happens with genes on the sex chromosomes), polygenetic traits (traits determined by more than one gene), linked genes (genes that often go together because they are located close to one another on the same chromosome), and more.

In this activity, we examine some human facial traits that are assumed to be single gene traits. The actual genetics is MUCH more complex. However a brief run-down is provided here (for photos of the traits listed below, see attachment at the bottom of the Human Traits activity):

  • Brown vs. non brown eyes – There are in fact at least 3 genes for eye color. The best understood is the brown vs. non brown gene in which brown in dominant to non-brown.
  • Freckles vs. no freckles – Freckles is dominant to no freckles by a single gene. Be sure to emphasize that this means have a LOT of PERMANENT freckles, not just a couple sun freckles that come and go depending on how much sunbathing you do.
  • Tongue rolling vs. non rolling – The ability to roll ones tongue into a U shape is dominant to not being able to.Dimples vs. no dimples – Cheek dimples that appear when a person smiles is dominant to not having dimples.
  • Attached vs. unattached earlobes – Unattached earlobes are dominant to attached earlobes.
  • Widow’s peak vs. straight hairline – Having a widow’s peak is dominant to have a straight hairline.
  • Cleft chin vs. smooth chin – Cleft chin is dominant to smooth chin.
  • Dark vs. light hair – Like eye color, hair color is a polygenetic trait. However, dark hair (black or brown) is dominant to light hair (blond or red) due to a single gene.
  • Curly vs. wavy vs. straight hair – Hair texture is a case of incomplete dominance. Heterozygotes end up with wavy hair.

There are a few traits to be cautious about using with students because people have a difficult time accurately recording traits. For instance, nearsightedness is a single gene trait with normal vision dominant to nearsightedness. However, kids often aren’t diagnosed with nearsightedness until late in adolescence. This leads to awkward questions such as, “Both my parents are nearsighted but I’m not. Does that mean I’m adopted?” Often teachers use round versus square shaped faces in which round faces are dominant to square faces. Both me and my students have difficulty categorizing faces as round or square, leading to much confusion. Other traits that are often difficult to categorize include: lip shape, eye spacing, eyelash length, eye slant, nose shape, and eyebrow thickness. Finally, be sure to warn students that in categorizing freckles, DO NOT COUNT sun freckles. Freckles means a very large number of freckles all over the nose and cheeks, whether you’ve been in the sun or not.

Student Prerequisites
Completion of the Human Traits activity.

2. Making Babies - Getting Ready

Getting Ready

  1. Make copies of the “Making Babies” handout.
  2. Set out pennies and colored pencils.

2. Making Babies - Lesson Plan

Lesson Plan

  1. Make sure each student has their “Human Traits Survey” completed and available.
  2. Pass out the “Making Babies” handout and assign partners for the activity.
  3. Read through the first page together, answering any questions students may have. Work through a couple examples of going from genotype to phenotype and back again with different traits. “If you cannot roll your tongue, what is your genotype?” “If your genotype is Rr for tongue rolling, what is your phenotype?”
  4. Help students fill in the table on page 2 with their phenotype and genotype. If the student has the dominant trait, assume that they are heterozygous unless they know for SURE that no relative has the recessive trait.
  5. Next, make gametes. Between the partners, one should make sperm, the other should make eggs. Each person will make 2 gametes by flipping a coin for each gene. We are assuming that the genes are not linked (even though hair color and eye color genes are, in fact, linked).
  6. Finally, students can create 2 babies by combining sperm #1 with egg #1 and combining sperm #2 with egg #2. Beside the genotype/phenotype descriptions, students should draw a picture of their children in color as they would appear in middle school.

2. Making Babies - Assessment

Assessment

  1. There are conclusion questions at the end of the handout.
  2. For homework, I assigned my students several pages from the book The Cartoon Guide to Genetics, by Lary Gonick and Mark Wheelis. Pages 37-55 deal with Gregor Mendel and inheritance patterns. The questions I asked include:
  • Who was Gregor Mendel?
  • In one experiment, Mendel crossed a tall pea plant with a short pea plant. What kind of eggs and pollen are produced? What is the genotype of the baby plant? What is the phenotype of the baby plant?
  • Next, he took these tall hybrids and bred them together. How many of these grandchild plants were tall? How many of these grandchild plants were short? Explain how it is possible for 2 tall pea plants to have a short baby.
  • Why were Gregor Mendel’s experiments important?
  • A brown eyed mom and a blue eyed dad have a blue eyed baby. What is the genotype of the baby? What is the genotype of the dad? What are two possible genotypes for the mom? Which genotype must she be to have a blue eyed baby? Explain why she must be this genotype.

Going Further

  1. Try the Dragon Genetics project.
  2. Have students model the mitosis and meiosis. My favorite mitosis/meiosis lesson is written by the Biology Lessons site from San Diego State University. The mitosis activity models the stages of mitosis with plastic utensils as chromosomes. Continue using the plastic utensil chromosomes to model meiosis OR you can add in the idea of crossing over by switching to modeling clay and yarn (see crossing over activity). Download the handout at the bottom of this page for an outline of the mitosis and meiosis process on which I had my students take notes.
  3. Make plant babies! Raise Wisconsin Fast Plants in the classroom and cross-fertilize different strains (hairy x hairless or tall x short). Study the inheritance of plant traits over several generations. For information on how to grow Fast Plants in the classroom, see the Raising Plants project in the Physiology Box.

2. Making Babies - Sources and Standards

Sources
This lesson was adapted from a lesson by Katie Ward of Aragon High School in San Mateo. After trying Katie’s version with my students, I found several other similar activities on the web. For instance, see the Making Babies lab written by Kevin Hartzog of Thurgood Marshall Academic High School. Kevin Hartzog's website Stars and Seas is extraordinary! With lots of other great lessons and ideas. Also recommended is this Making Babies lab from Friends Academy .

For information about Mendelian genetics, see:

For more information on the inheritance of human traits such as eye color, hair color, and tongue rolling, see:

  • The Eye Color Calculator from the Tech Museum of Innovations’ online genetics exhibit is very fun with good genetics background information. In addition, their “Ask a geneticist” area contains great Q&A about other human traits such as hair color, addiction, ADHD, genetic diseases and more. Do your students have a question that you can’t answer? Post a question!
  • For a searchable database of human genes and relevant scientific studies, John Hopkins has a fantastic resource, the Online Mendelian Inheritance in Man website.
  • The Wikipedia article on dominance relationships including a short list of traits governed by simple dominance.
  • Bill Kendrick created a very fun “Gene Machine” that predicts your genotype based on inputting the phenotypes of yourself, your mother and your father.

Standards
Grade 7
Genetics
2. A typical cell of any organism contains genetic instructions that specify its traits. Those traits may be modified by environmental influences. As a basis for understanding this concept:
b.     Students know sexual reproduction produces offspring that inherit half their genes from each parent.
c.     Students know an inherited trait can be determined by one or more genes.
d.     Students know plant and animal cells contain many thousands of different genes and typically have two copies of every gene. The two copies (or alleles) of the gene may or may not be identical, and one may be dominant in determining the phenotype while the other is recessive.

Grades 9-12
Genetics
2. Mutation and sexual reproduction lead to genetic variation in a population. As a basis for understanding this concept:
a.     Students know meiosis is an early step in sexual reproduction in which the pairs of chromosomes separate and segregate randomly during cell division to produce gametes containing one chromosome of each type.
b.     Students know only certain cells in a multicellular organism undergo meiosis.
c.     Students know how random chromosome segregation explains the probability that a particular allele will be in a gamete.
d.     Students know new combinations of alleles may be generated in a zygote through the fusion of male and female gametes (fertilization).
e.     Students know why approximately half of an individual's DNA sequence comes from each parent.
f.     Students know the role of chromosomes in determining an individual's sex.
g.     Students know how to predict possible combinations of alleles in a zygote from the genetic makeup of the parents.

3.   A multicellular organism develops from a single zygote, and its phenotype depends on its genotype, which is established at fertilization. As a basis for understanding this concept:
a.     Students know how to predict the probable outcome of phenotypes in a genetic cross from the genotypes of the parents and mode of inheritance (autosomal or X-linked, dominant or recessive).
b.     Students know the genetic basis for Mendel's laws of segregation and independent assortment.
c.     * Students know how to predict the probable mode of inheritance from a pedigree diagram showing phenotypes.

3. DNA Extraction

Strawberry DNA: The cloudy substance in the upper layer is strawberry DNA.Strawberry DNA: The cloudy substance in the upper layer is strawberry DNA.Summary
What is DNA? What does it look like? In this activity, students extract DNA from strawberries using diluted dish soap and alcohol. Suddenly this mysterious secret of life can be seen materializing out of strawberry juice right in front of students’ eyes. The long tangled DNA strands that ultimately form may be collected using a bamboo skewer or glass stirring rod. The DNA may even be saved in a necklace made from an eppendrof tube, alcohol and string.

Objectives
Can extract DNA.
Can recognize that DNA is found in all cells.
Can explain the steps needed to isolate DNA from a cell.
Can begin to describe the structure of DNA – that it is a long, invisibly thin polymer.

Vocabulary
DNA
Nucleus
Cell
Membrane

AttachmentSize
3dna_extraction.doc52.5 KB

3. DNA Extraction - Logistics

Time
40 minutes

Grouping
individual

Materials
Each student needs:

  • 1 fresh strawberry (frozen strawberries also work fine although they are not nearly as much fun to eat)
  • 1 ziplock bag
  • 1 15 ml centrifuge tube or 5 oz paper bathroom cup
  • 1 clear glass or plastic test tube
  • 1 paper towel
  • 10 ml extraction buffer (see recipe below)
  • 1 bamboo skewer or glass stirring rod (DNA tends to stick more fiercely to bamboo than wood – however, bamboo is MUCH cheaper)

Extraction buffer recipe:

  • 450 ml distilled water
  • 10 g table salt
  • 50 ml Dawn dishwashing detergent

Optional for making necklaces:

  • 1 1.5 ml Eppendorf tube (also known as microcentrifuge tubes, available from Science Kit and Boreal Labs at $13.25 for 500 tubes)
  • 50 cm of string or yarn

For the whole class to share:

  • clean food bowl
  • clean toothpicks for eating strawberries
  • 90% ice cold rubbing alcohol or ethanol
  • eye droppers for dispensing solutions

Setting
Classroom

3. DNA Extraction - Background

Teacher Background
This activity should be part of the standard repertoire of any teacher who teaches genetics. It is essential for students to prove to themselves that DNA exists and that it can be extracted from any cell. Strawberries are used in this activity because they are octaploid, meaning they have 8 copies of every gene rather than the usual 2; thus providing prodigious quantities of DNA to extract. Naturally, strawberries are also relatively inexpensive and readily available. Other sources of DNA to experiment with include kiwis, bananas, and calf thymus.

The DNA molecule is an invisibly thin, very long strand. The DNA found in each human cell is almost 2 meters long. If all the DNA in a human adult (that’s 100 trillion cells) were laid end to end, the DNA would stretch 113 billion miles. That would take you to the sun and back 610 times. Even though DNA is invisible to the naked eye, no microscopes are needed! The reason is that you release so many DNA strands that they tangle together into a thick cable, visible without magnification. For example, it would be the same as if you took a thin piece of thread and held it up on the far end of the hallway. You probably wouldn’t be able to see the thread from that distance. However, if you took the thread and tangled it up with a hundred thousand other threads, you would be able to see the tangled clump from far away because there is so much of it.

The process itself is fairly straightforward. First the cell walls are broken open by smashing the strawberries in a ziplock bag. Next, detergent is used to dissolve the cell and nuclear membranes. The membranes are made of lipids (fat) and the detergent will cut through the membrane just like it cuts through grease on a dirty plate when washing dishes. Some salt is present in the detergent solution in order to match the osmolarity of the cells.

Now you have a big mixture of smashed cell walls, dissolved membranes, loose DNA and random other cell parts. This mixture is filtered through paper towels. Finally, you take advantage of the fact that DNA is soluble in water but not in alcohol. In fact, alcohol makes DNA clump together. Thus a layer of alcohol laid on top of the filtrate. Any DNA that contacts the alcohol will clump together, pulling the rest of the DNA strand along behind it. Soon you should see gossamer white strands of DNA bubbling their way up from the red strawberry extract.

The DNA may be collected by twirling a bamboo skewer or glass stirring rod in the solution. The DNA will spool itself around the skewer and can be pulled out of the solution. To keep some DNA, students may fill an eppendorf tube with alcohol and place their spooled DNA into the container. Lay the string on the hinge holding the cap to the tube and close the lid. The string forms a necklace with the eppendorf and enclosed DNA as a pendant. Top off the alcohol in the pendant and you can keep the DNA indefinitely.

Student Prerequisites
Some cell biology experience (enough to know that DNA is located in the nucleus of a cell and that membranes are made of lipids) is useful. If students are not aware of these fact, expect to spend at least 10 minutes longer teaching these ideas before starting the extraction.

3. DNA Extraction - Getting Ready

Getting Ready

  1. Purchase strawberries, enough for each student to have one. (They will eat half and use the remainder to extract DNA.)
  2. Prepare the extraction buffer.
  3. Put the alcohol in the freezer or on ice.
  4. Wash the strawberries and remove the green tops. Cut each strawberry in half. Put half in a clean food bowl for students to eat. Put the remainder in a separate bowl for students to extract DNA from.
  5. Set out the remainder of the materials.

3. DNA Extraction - Lesson Plan

Lesson Plan

  1. Have students write down a few sentences to describe what DNA is and what they think DNA looks like. After this lab or the series of DNA modeling activities, they will come back to this naive description to revise their answers with a more scientific one.
  2. Draw a diagram on the board showing DNA (as a long tangled thread) within the nucleus of a cell. Label the DNA, nucleus, cell membrane, and cell wall. Remind (or teach) students about basic cell structure.
  3. Tell students that they will be extracting the DNA from a strawberry and will then be able to look at the DNA. Briefly describe the process explaining the purpose of each of the steps.
  4. Pass out ziplock bags and strawberries. Tell students there are strawberries to eat after the lab is cleaned up.
  5. Students should put the strawberry in the bag, squeeze out most of the air and seal the bag. The strawberry can then be crushed into juice and pulp. Try to squish all of the chunks into an even, smooth puree. Warn students not to pound the strawberry on the table or risk the bag bursting and getting strawberry pulp all over themselves and the classroom.
  6. Next, open the bag and add 10 ml of extraction buffer (approximately 10 eyedroppers full). Seal the bag again and gently mix the strawberry juice with the extraction buffer. Warn students not to mix too vigorously or it will generate a lot of bubbles and can’t be filtered effectively. Use a gentle tilting back and forth motion while lightly squeezing the bag.
  7. Set up a filtration system. I had students wrap a paper towel around their finger then put their paper-wrapped finger into the mouth of the 15 ml tube or 5 oz cup. When you remove your finger, the paper towel should form a well into which the strawberry juice can be poured.
  8. Carefully pour the extract into the well in the paper towel. Allow the juice to filter through the towel into the container below. Let it drip for 3-5 minutes. Do not squeeze the towel or you will create lots of bubbles, disrupting the interface needed in the next step.
  9. The paper towels can be put inside the ziplock bags and thrown away.
  10. Carefully transfer liquid from the 15 ml tube or cup into the clear test tube until the test tube is about a third full.
  11. Slowly add 3 ml (3 eye droppers full) of ice cold alcohol to the test tube. The alcohol should be added so that it trickles down the side of the tube before pooling on top of the strawberry extract. You should end up with a red bottom layer and a clear top layer.
  12. Have the students make observations of anything going on in the clear alcohol layer. You may wish to have students write down observations at this point.
  13. After 2-3 minutes, a skewer or stirring rod can be inserted into the tube and gently swirled around. This will spool the DNA around the stick. The DNA can be pulled out of the tube and stored in a microcentrifuge tube filled with some alcohol. Students may safely touch the DNA although the DNA should NOT be tasted under any circumstances.
  14. By trapping a piece of string in the lid of the microcentrifuge tube, students can wear their DNA home as a necklace.
  15. Have students clean up their areas. Nicely cleaned tables and washed hands may be rewarded with a piece of strawberry to eat.

3. DNA Extraction - Assessment

Assessment

  1. Have students answer summary questions about the extraction.
  • Why is it necessary to mash the strawberries?
  • What is the purpose of the detergent?
  • What is the purpose of the salt?
  • Name a liquid that DNA is not soluble in.
  • Is the DNA that you extracted pure? What else might be attached to the DNA?
  • Why might some people get more DNA than others?
  • Can you see a single strand of DNA without a microscope? Explain how you were able to see the DNA in this experiment without magnification.


Going Further

  1. Make models of DNA (see DNA Models lesson).
  2. Try to isolate DNA from other soft fruits and vegetables. This may even be done as homework. Compare the DNA yields and discuss why different plants would give different results.

3. DNA Extraction - Sources and Satndards

Sources
There are numerous write ups for this experiment available on the internet and elsewhere. I first experienced this lesson through UCSF’s Science and Health Education Partnership. I then tried it with Carolina Biological .

The estimates of the length of DNA in a human cell and the number of cells in the human body were taken from Wikipedia (from the Genome and Cell Biology articles).

Standards
Grade 7
Genetics
2. A typical cell of any organism contains genetic instructions that specify its traits. Those traits may be modified by environmental influences. As a basis for understanding this concept:
e.    Students know DNA (deoxyribonucleic acid) is the genetic material of living organisms and is located in the chromosomes of each cell.

Grades 9-12
Genetics
5. The genetic composition of cells can be altered by incorporation of exogenous DNA into the cells. As a basis for understanding this concept:
a. Students know the general structures and functions of DNA, RNA, and protein.

4. DNA Models

Summary
DNA structure: click on the image to see it rotateDNA structure: click on the image to see it rotateIn this activity, students “discover” the structure of DNA by playing with puzzle pieces representing the component pieces of the DNA molecule: the sugar deoxyribose, phosphate groups, and the 4 nucleic acids (adenine, thymine, cytosine and guanine). The process the students go through in putting the puzzle together resembles the way James Watson and Francis Crick deduced the molecular structure of DNA by manipulating molecular models of the component pieces (and a heavy reliance on the prior experimental work of Rosalind Franklin, Maurice Wilkins, and Erwin Chargaff). The model created by the students makes a lovely classroom decoration and reference for discussing DNA replication, transcription and translation.

Objectives
Can model and describe the general structure of DNA.
Can apply base pairing rules to assemble a DNA molecule.
Can infer that the sequence of the nucleic acids in DNA is the key to how DNA provides instructions to the cell.
Can relate this DNA puzzle activity to Watson and Crick’s original discovery of the structure of DNA.

Assembling the DNA puzzleAssembling the DNA puzzleVocabulary
DNA
Deoxyribose
Phosphate
Nucleic acid
Adenine
Thymine
Cytosine
Guanine
Base pairs
Nucleotide

AttachmentSize
4dna_models.doc59.5 KB
dna_pieces.pdf1.09 MB

4. DNA Models - Logistics

Time
30 minutes to cut DNA model pieces (It is possible to assign each student a sheet of puzzle pieces to cut out as homework the night before.)
20 minutes to assemble puzzle
10 minutes to tape puzzle together
10-20 minutes to discuss DNA structure and the discovery of the DNA structure

Grouping
Individual students gradually linking their puzzles together to create a long strand.

Materials

  • Scissors
  • Copies of puzzle pieces, each on a different colored paper. For a group of 30 students you will need:
    • 4 copies each of A, C, T, and G
    • 8-9 copies of P
    • 11-12 copies each of S-deoxyribose
  • Several rolls of Scotch tape.
  • Optional: several rolls of 2” packing tape (use if you want to “laminate” the models for display).
  • Bins or trays on which to keep the puzzle pieces. One for every 4-6 students.

Setting
classroom

4. DNA Models - Background

Teacher Background
Although DNA was isolated in the 1800s, it was not until the 1900s that scientists believed DNA might store genetic information. By 1929, the 3 major components – the sugar deoxyribose, a phosphate group, and a nucleic acid – had been identified. Furthermore, it was known that the phosphate groups linked the molecule together in a long polymer, however it was assumed that the chains were short and that the bases repeated in the same fixed order.

Towards the late 1940s, more and more came to be known. Erwin Chargaff noticed that in any species he studied, the quantity of adenine was always the same as the quantity of thymine while the amount of guanine was the same as the amount of cytosine. This came to be known as “Chargaff’s ratios”. But what did these rations mean? At around the same time, X-ray diffraction data indicated that DNA was coiled in a helical structure. But how many chains were part of the helix? Did the nucleic acids point in toward the center our face out?

Rosalind Franklin: Rosalind FranklinRosalind Franklin: Rosalind FranklinJames Watson and Francis Crick deduced the structure of DNA in 1953. There were several events that helped them put together the puzzle. First and foremost, the meticulous X-ray diffraction work of Rosalind Franklin and Maurice Wilkins clearly illustrated that the DNA molecule consisted of 2 strands, a double helix, with the nucleic acids on the inside of the molecule. Moreover, the distance between the strands and the pitch of the helix could be precisely measured. With this information, Watson and Crick were able to build a model of the sugar-phosphate backbone of DNA.

The final step of the solution required the use of cardboard models of the 4 nucleic acids. Watson and Crick cut out precise shapes for each nucleic acid. On the hunch that Chargaff’s rule implied a pairing between adenine-thymine and cytosine-guanine, they played with their puzzle pieces to see how they might fit together. They realized that in just the right orientation, adenine-thymine and cytosine-guanine pairs were almost identical in shape, thus providing equally spaced rungs between the 2 backbones of the ladder.
Watson and Crick DNA model: Physical model built by James Watson and Francis Crick to deduce the structure of DNA. Currently on display in the National Science Museum of London.Watson and Crick DNA model: Physical model built by James Watson and Francis Crick to deduce the structure of DNA. Currently on display in the National Science Museum of London.
Watson and Crick published their work in 1953 alongside an article by Franklin and Wilkins showing the X-ray diffraction data. In 1962, Watson, Crick and Wilkins were awarded the Nobel Prize for discovering the structure of DNA. By that time, Franklin had died of ovarian cancer. Since Nobel prizes are not awarded posthumously, Franklin could not share in the honor.

Thus the structure of DNA can be said to be composed of two sugar-phosphate backbones, oriented in opposite directions to one another (notice how the sugars on one side are upside-down compared to the sugars on the other strand). The sugars are then attached to a nucleic acid. The nucleic acids are paired such that adenine is always matched to thymine with 2 hydrogen bonds while guanine is always matched to cytosine with 3 hydrogen bonds. A matching pair of nucleic acids is called a base pair. The assembly of one phosphate, sugar and nucleic acid is called a nucleotide.

Student Prerequisites
None

4. DNA Models - Getting Ready

Getting Ready

  1. Make photocopies of puzzle pieces, each on a different colored paper.
  2. Have students cut out 1 or 2 sheets per person, possibly as homework the night before the activity.

4. DNA Models - Lesson Plan

Lesson Plan

  1. Tell students that today they will be assembling a DNA puzzle. Show students each of the pieces and tell them what the letters on each represent. If you want, tell students the beginning of the DNA discovery story, especially how Watson and Crick created puzzle pieces to represent the different parts and tried to fit the pieces together in a way that made sense with the data that was known at the time.
  2. Pass out the puzzle pieces and instruct students to build a DNA molecule. Very little instruction is needed since it is very difficult to put together wrong. The only errors I’ve seen are students who try to flip the pieces so that the letters are hidden and students who try to fit the triangle indent of “T” with the triangle point of “S”.
  3. Circulate around the room and help students as needed. When most students have assembled a molecule 4-5 base pairs long, have students start connecting their molecule together with their neighbors’. At this time, they should also begin taping their molecules together with Scotch tape.
  4. When all the students have merged their pieces into a single long strand, have several students hold up the assembled molecule at the front of the class. Draw conclusions and observations from the group. For instance:
    • What do you notice about the structure overall? What does it look like?
    • How do the two sides of the ladder compare?
    • What are the rungs of the ladder made of?
    • Which nucleic acid pairs with which?
    • How were each person’s individual DNA the same as others’ DNA? How were they different? In what ways you think the real DNA in each person’s cells is the same? In what ways do you think it is different?
  5. Relate the activity back to the real story of the discovery of the DNA structure.
  6. Complete the discussion with a formal definition of the vocabulary words such as base pair and nucleotide.
  7. Optional: “Laminate” the models by covering both sides of the model with packing tape. The model may then be twisted into a helix and hung from the ceiling or walls of the room. You may want to hold off on laminating your model until after discussing DNA replication, transcription, and translation (see Going Further ideas).

Laminated DNA paper puzzleLaminated DNA paper puzzle

4. DNA Models - Assessment

Assessment

  1. Have students draw, label and color pictures of DNA.
  2. Have students build other 3D models of DNA using different materials (beads, candy connected with toothpicks, Styrofoam peanuts, etc.). See the DNA Jewelry Project for one idea or leave the project open ended and have students select their own materials and design.

Going Further

  1. Use the DNA models to illustrate the process of DNA replication, transcription and translation. See Protein Factory lesson.
  2. Show video clips of DNA structure or create a webquest about the search for the DNA structure. The best animations I have seen are available at DNA Interactive. For a great series of web pages telling the story of the discovery, check out the “Finding the Structure” section of DNA Interactive under the main tab “Code”.
  3. For advanced classes such as AP Bio, the 2 hour movie “The Race for the Double Helix”, starring Jeff Goldblum, is a well done dramatization of the many scientists competing against one another in search of the structure of DNA. See this review by Mark Leeper with accompanying discussion questions.

4. DNA Models - Sources and Standards

Sources
This activity was adapted from a DNA model designed by Lori Lambertson of the Exploratorium Teacher Institute.

For additional background materials, see:

  • Wikipedia article on DNA.
  • Read a copy of Watson and Cricks original 1953 article.
  • For the best online DNA resource I’ve seen, go to DNA Interactive. You will find interviews with scientists, gorgeous computer animations, lesson plans and fabulous web activities.
  • The classic book, The Double Helix: a personal account of the discovery of the structure of DNA by James Watson.
  • An alternative view of the role played by Rosalind Franklin, Rosalind Franklin and DNA by Anne Sayre.

Standards
Grade 7
Cell Biology
1. All living organisms are composed of cells, from just one to many trillions, whose details usually are visible only through a microscope. As a basis for understanding this concept:
c.     Students know the nucleus is the repository for genetic information in plant and animal cells.

Genetics
2. A typical cell of any organism contains genetic instructions that specify its traits. Those traits may be modified by environmental influences. As a basis for understanding this concept:
e.    Students know DNA (deoxyribonucleic acid) is the genetic material of living organisms and is located in the chromosomes of each cell.

Grade 8
Chemistry of Living Systems (Life Sciences)
6. Principles of chemistry underlie the functioning of biological systems. As a basis for understanding this concept:
c.     Students know that living organisms have many different kinds of molecules, including small ones, such as water and salt, and very large ones, such as carbohydrates, fats, proteins, and DNA.

Grades 9-12
Genetics
5. The genetic composition of cells can be altered by incorporation of exogenous DNA into the cells. As a basis for understanding this concept:
a. Students know the general structures and functions of DNA, RNA, and protein.
b. Students know how to apply base-pairing rules to explain precise copying of DNA during semiconservative replication and transcription of information from DNA into mRNA.

5. Secret Codes

Example secret DNA codeExample secret DNA code

Summary
Kids love secret codes and secret messages. In this activity, kids first discover how codes work by reading and writing secret messages written in Morse code. Next, they make up their own secret codes and trade messages written in their self-created code. Finally, students learn how DNA codes for a “secret” protein message in a two step coding system – the genetic code. Since each of the 20 amino acids has a one letter abbreviation, student can discover the secret protein “messages” encoded in a DNA strand. Several secret DNA messages are provided for students to decode under the assessments section. For homework, students can be challenged to write a secret message to a friend using the genetic code.

Objectives
Can explain how DNA codes for a sequence of amino acids.
Can begin to explain some of the differences between DNA and RNA.
Can begin to describe the process of transcription and translation.

Vocabulary
DNA
Messenger RNA
Ribosome
Amino acids
Protein
Codon
Morse code
Genetic code
Transcription
Translation

AttachmentSize
5secret_codes.doc48.5 KB
codes_handout.doc43 KB

5. Secret Codes - Logistics

Time
45-55 minutes

Grouping
Individual

Materials

  • Copies of Secret Codes handout
  • Optional: internet access and a computer projection system to show students 2 web-based videos of transcription and translation from DNA Interactive.

Setting
classroom

5. Secret Codes - Background

Teacher Background
The genetic code is a set of rules that guide how the sequence of DNA nucleotides is read by a cells machinery and turned into a sequence of amino acids that make up a protein. Incredibly, nearly all living things use the same genetic code!

To understand how DNA provides the instructions for making proteins, one first needs to understand a little about what a protein is. A protein, like DNA, is a polymer (a long molecule that is a chain of smaller repeating subunits). The subunits in proteins are called amino acids. There are 20 different amino acids that can be linked together in an infinite array of sequences of different lengths. These chains of amino acids form the proteins that do all the work in our bodies – building cells, generating energy, transporting materials, and more. For this activity, it is important to note that each amino acids has been assigned a single letter abbreviation which allows students to create protein “words” and “messages” with different sequences of amino acids.

The DNA in a cell can be divided into functional units called genes. Each gene provides the instructions for making one protein. Thus, one can think of a gene as a long paragraph describing how to make a protein. The “letters” in the paragraph are the nucleotides (the A’s, T’s, C’s and G’s). The “words” within the gene are made of a sequence of 3 nucleotides, each of which specifies one amino acid in the protein. For instance, the DNA sequence, TAC, specifies the amino acid, methionine. Each nucleotide triplet that codes for an amino acid is called a “codon”.

The process of protein synthesis (reading the DNA codons and translating it into a sequence of amino acids) is a gorgeous, choreographed process involving many steps. For more detail on protein synthesis and the molecules involved, see the background section in the Protein Factory activity.

For the purposes of this activity, one needs to know that the DNA is trapped in the nucleus (at least in plant and animal cells) while the protein making apparatus, the ribosome, is located outside the nucleus in the cytosol. Therefore, a messenger molecule, messenger RNA, is used to copy the DNA message and bring it to the ribosome. RNA is closely related to DNA. They both are polymers of nucleotides with a sugar-phosphate backbone. The differences are that RNA is single stranded, while DNA is double stranded. Furthermore, RNA uses the nucleic acid, uracil, instead of thymine. Finally, instead of the sugar deoxyribose in the backbone, RNA uses the sugar ribose.

Protein synthesis can be summarized in 2 steps:

  1. One of the 2 strands of DNA is transcribed into a single stranded messenger RNA, which carries the DNA message to the ribosome.
  2. The ribosome reads the messenger RNA and assembles the appropriate sequence of amino acids.

In this activity, students become familiar with the idea of a coded message by practicing with Morse code. Morse code uses a sequence of dashes and dots to represent the letters of the alphabet, numbers and punctuation. It was developed in the 1830’s for early telegraph and radio communications. Once they get the idea, they have an opportunity to make up their own secret codes, with a different symbol (letter, number, picture) to represent each letter of the alphabet. They write a message to a classmate in their secret code. The keys and coded messages are traded and students can decode each others’ messages.

Then, they are told about how a strand of DNA can be turned into RNA and then into a string of amino acids. Using the one letter abbreviations of the amino acids, secret messages may be written and decoded using the genetic code. The idea of a genetic code can be compared to Morse code and their self-created codes. I have found that this activity makes the big picture of protein synthesis much easier for students to understand than jumping straight into the details of the molecules involved and how they all interact.

Student Prerequisites
A solid understanding of DNA structure is essential. A basic understanding of what a protein is and its structure is helpful but not required.

5. Secret Codes - Getting Ready

Getting Ready

  • Make copies of the Genetic Code handout.

5. Secret Codes - Lesson Plan

Lesson Plan

  1. Ask the students, “If you were a spy, how would you write a message to headquarters in a way that if the enemy intercepted it, they would not know what the message said?” Students will instantly respond with using a secret code. Ask for clarification of what a secret code is and how it is used.
  2. Give students the handout. Briefly discuss what Morse code is and how it is used.
  3. Have students try to decode the message at the bottom of the page. The secret message says, “I love learning about genetics!” Make up your own messages for students to decode as additional practice.
  4. Next, have students make up their own secret code by writing a different symbol (letter, number, picture) next to each letter of the alphabet on the right hand side of the page. Students can use their personal code to write a secret message to a friend on the bottom of the page.
  5. Collect the handouts when students are done, shuffle them, and redistribute them so students can practice decoding someone else’s message.
  6. Now that students are fluent with coding and decoding messages, introduce how DNA is a code for making proteins. Describe protein structure. Outline the 2 basic steps of the protein synthesis process: 1) DNA is transcribed into messenger RNA and 2) ribosome reads the RNA and assembles a chain of amino acids using the RNA codons.
  7. Have students flip their handouts over and look at the genetic code. Go over the examples, showing how the DNA codes for a protein message with a two step decoding process. First translate the top line of the DNA into RNA. Then use the table to identify the sequence of amino acids that matches each 3 nucleotide codon. The secret message at the bottom of the page says, “I like math”.
  8. Give students additional DNA codes to solve. See the Assessment section for ideas or create your own. Since there are only 20 amino acids, some letters cannot be used (B, J, O, U, X, Z).
  9. Optional: Show students the video of transcription and translation from the DNA Interactive website (click on the “Code” tab, then click the “Reading the Code” tab and finally click the “Putting it Together” tab.)

5. Secret Codes - Assessment

Assessment

  1. Have students decode one or more of the following DNA messages:
    • “Genetics”
      C C G C T T T T A C T C T G A T A G A C G A G T
      G G C G A A A A T G A G A C T A T C T G C T C A
    • “Science”
      T C G A C A T A T C T T T T A A C G C T T
      A G C T G T A T A G A A A A T T G C G A A
    • “DNA is neat”
      C T A T T G C G C T A G A G T T T G C T T C G T T G G
      G A T A A C G C G A T C T C A A A C G A A G C A A C C
    • “Why me?”
      A C C G T A A T A T A C C T C ?
      T G G C A T T A T A T G G A G
  2. Have students write their own secret word or short message using the genetic code. Warn them that some letters (B, J, O, U, X, Z) cannot be used. Trade these messages the following day.

Going Further

  1. Go into the details of the transcription and translation process. See the Protein Factory lesson and Comic Strip Assessment activities

5. Secret Codes - Sources and Standards

Standards
Grade 8
Chemistry of Living Systems (Life Sciences)
6. Principles of chemistry underlie the functioning of biological systems. As a basis for understanding this concept:
c. Students know that living organisms have many different kinds of molecules, including small ones, such as water and salt, and very large ones, such as carbohydrates, fats, proteins, and DNA.

Grade 9-12
Genetics
4. Genes are a set of instructions encoded in the DNA sequence of each organism that specify the sequence of amino acids in proteins characteristic of that organism. As a basis for understanding this concept:
a. Students know the general pathway by which ribosomes synthesize proteins, using tRNAs to translate genetic information in mRNA.
b. Students know how to apply the genetic coding rules to predict the sequence of amino acids from a sequence of codons in RNA.
e. Students know proteins can differ from one another in the number and sequence of amino acids.

6. Protein Factory

Summary
Using a DNA model like the one created in the DNA Models lesson, students take on the role of various parts of the cell in order to model the process of protein synthesis. Each student receives a card describing, step by step, what s/he should be doing. In a class of 30:

Objectives
Can explain how DNA codes for a sequence of amino acids.
Can explain the differences between DNA and RNA.
Can describe the process of transcription and translation.

Vocabulary
DNA
Nucleotide
RNA polymerase
Promotor
Uracil
Messenger RNA
Ribosome
Transfer RNA
Amino acids
Protein
Genetic code
Codon
Anticodon
Transcription
Translation

AttachmentSize
6protein_factory.doc59 KB
factory_instructions.doc37 KB
protein_pieces.pdf638.23 KB

6. Protein Factory - Logistics

Time
45-55 minutes

Grouping
Whole class.

Materials

  • Copies of the Genetic Code handout (see Secret Codes activity)
  • 1 assembled paper DNA model, 60 base pairs long (1 codon per student acting as a tRNA)
  • Copies of Factory Instructions (follow the teacher instructions on the top of the page for how many copies of each to make)
  • Copies of DNA puzzle pieces, each on a different colored paper. For a group of 30 students you will need:
    • 4 copies of S-ribose
    • 3 copies of P-phosphate
    • 2 copies of A, C, G, and U
    • 2 copies of amino acid
    • 10 copies of transfer RNA
    • You also need several DNA model puzzle pieces to create the promotor, translation start, and translation stop sequences. Hopefully, you have some left over from the DNA model activity:
    • 30 S-deoxyribose pieces (1 sheet)
    • 30 P-phosphate pieces (1 sheet)
    • 10 A, C, G, and T pieces (half a sheet)
  • Scissors
  • 8 rolls of Scotch tape
  • Bins or trays on which to keep the puzzle pieces.

Setting
classroom

6. Protein Factory - Background

Teacher Background
The process of turning DNA into protein is called the “central dogma of molecular biology” because it is the foundation of all modern genetics, biotech and pharmacology. There are 6 major players in the process.

  1. DNA – the blue print for construction of specific proteins. A section of DNA that codes for a protein is called a gene. More on the structure of DNA can be found in the background section of the DNA Models activity.
  2. RNA polymerase – an enzyme responsible for assembling a strand of RNA from a DNA template. It is formed from an assembly of several different individual proteins with various roles.
  3. Messenger RNA – temporary courier of information that brings a copy of the information encoded in the DNA to the ribosome where the proteins are actually made. More on the differences between RNA and DNA can be found in the background section of the Secret Codes activity
  4. Ribosome – a fairly complex organelle that is like a protein factory. It assembles a chain of amino acids using the messenger RNA as a template. More on the genetic code that governs which amino acids pair with what RNA sequence may be found in the background section of the Secret Codes activity.
  5. Transfer RNA – a small length of RNA (less than a hundred base pairs long) that transfers a specific amino acid to the growing protein chain within a ribosome. Each transfer RNA has a site where an amino acid can bind and a special 3 nucleotide sequence celled the “anticodon.” The anticodon matches a 3 nucleotide sequence on the messenger RNA molecule called the “codon”.
  6. Protein – the primary building material of cells. Proteins constitute most of the dry mass of a cell and execute nearly all cell functions. Proteins are long single stranded chains constructed of 20 different building blocks called amino acids.

Transcription and translation: Illustration from Radboud University NijmegenTranscription and translation: Illustration from Radboud University NijmegenThere are 2 major steps in the protein synthesis process. The first is the synthesis of messenger RNA in a process known as transcription. This process is similar to DNA replication, except that only a tiny portion of one strand is copied and it is copied into a single-stranded RNA molecule, not a double stranded DNA molecule.

To start transcription, RNA polymerase binds to a specific DNA sequence known as a promotor. Promotors sequences are very diverse, however, generally are found in the stretch of DNA in front of the gene and contain a place for RNA polymerase to bind as well as a transcriptional start sequence that indicates where transcription should begin. They range in length from less than a hundred base pairs to several thousand base pairs. Many promotor sequences contain the sequence TATAAA, known as a TATA box by biologists. This TATAAA sequence is used in this activity to indicate where the RNA polymerase should bind and begin transcription.

Once, the RNA polymerase binds to the promotor, it follows along the DNA, unzipping the base pairs, reading one of the two DNA strands, matching an RNA nucleotide to each DNA nucleotide, and assembling a messenger RNA molecule. The RNA polymerase continues moving along the DNA until it reaches a specific terminator sequence, at which point it releases the messenger RNA and disassembles. Messenger RNA molecules may extend over 2 million bases in length. At this point, the messenger RNA travels out of the nucleus to the ribosome where proteins are actually made.

This second step of the protein synthesis process is known as translation. First, a ribosome assembles around the messenger RNA molecule. Translation always begins at the messenger RNA sequence AUG. The messenger RNA then feeds its way through the ribosome like a tape. As it proceeds, each codon on the messenger RNA is matched to a transfer RNA. The ribosome forms bonds between the amino acids carried by the transfer RNAs and the empty transfer RNA molecules detach and float away. Gradually, the amino acid chain grows longer and longer until a stop sequence (UAG, UAA, or UGA) is reached. At that point, the protein is released.

From here, the protein may go through many stages of further processing. Depending on the sequence of amino acids, some parts of the protein like water and some curl away from it. Thus, the protein will fold itself up to protect the water-hating parts of the protein from the surrounding cytosol. In addition, proteins may be cut, spliced, joined together, packaged and reshaped into a final functional protein.

Student Prerequisites
Some basic introduction to the protein synthesis process (see Secret Codes lesson).

6. Protein Factory - Getting Ready

Getting Ready

  1. If not already assembled, put together a DNA model 60 base pairs long. Check to make sure that none of the stop codons (UAG, UAA and UGA) would be part of the messenger RNA coded by the sequence. Flipping the DNA molecule over or adding 1 or 2 extra bases on one end of the DNA sequence may solve the problem.
  2. To one end of the DNA model, add the following sequence (this is your promotor sequence to start transcription and your AUG start sequence to start translation):
    T A T A A A C T T A C x x x ...
    A T A T T T G A A T G x x x
  3. To the opposite end of the DNA model, add the following sequence (this is your stop codon).
    ... X X X A T C
        X X X T A G
  4. Optional: work out for yourself what the sequence of amino acids would be for the DNA molecule you have. You want to check to make sure that there are no stop codons (UAG, UAA and UGA) within the messenger RNA.
  5. Make photocopies of the Factory Instructions handout. Follow the detailed directions at the top of the page.
  6. If not already given to students, make photocopies of the Genetic Code handout.
  7. Make photocopies of the puzzle pieces, each on a different colored paper.
  8. Have students cut out 1 or 2 sheets of puzzle pieces per person, possibly as homework the night before the activity.
  9. Place S-ribose, P and half of the A, C, G, and U pieces in one bin for the students playing the role of messenger RNA.
  10. Place amino acid, transfer RNA and the remaining half of the A, C, G, and U pieces in several other bins (4-5 bins total for 20 students to share) for the students playing the role of transfer RNA.
  11. Designate one area of the classroom as the nucleus with the other areas as the cytosol.

6. Protein Factory - Lesson Plan

Lesson Plan

  1. Begin class with a secret DNA message for the students to decode (see assessment section of the Secret Codes lesson).
  2. Review the steps of the protein synthesis process: 1) DNA is transcribed into messenger RNA and 2) the RNA is translated into a sequence of amino acids based on 3 nucleotide codons.
  3. Give students more detailed background information on how the protein synthesis process works. Discuss the role of RNA polymerase and the ribosome. Describe how RNA polymerase recognizes where to start transcribing the gene (a promotor sequence) and how the ribosome knows where to start (AUG) and stop (UAG, UAA, or UGA) translating the messenger RNA.
  4. Give students an overview of the rest of the class period. Show students where the nucleus is and where the cytosol is.
  5. Assign students their roles. Each student should get an instruction card and the materials listed on their instruction card.
  6. Allow students performing the role of the messenger RNA to create RNA nucleotides. Allow students performing the role of the transfer RNA a few minutes to assemble their transfer RNA molecules.
  7. Restore silence to the classroom and begin the process. Have all the students watch as the process unfolds. You may want to describe what is going on at each step for the students that aren’t involved directly. Briefly:
    1. RNA polymerase finds the TATAAA promotor sequence on the DNA molecule.
    2. RNA polymerase unzips the DNA nucleotide after the promotor and finds a matching RNA nucleotide.
    3. RNA polymerase unzips the next DNA nucleotide and finds a matching RNA nucleotide.
    4. RNA polymerase joins the RNA nucleotides together.
    5. RNA polymerase continues unzipping, finding nucleotides, and joining them together until the end of the DNA molecule.
    6. DNA zips itself back up again.
    7. The newly assembled messenger RNA floats out of the nucleus to the ribosome.
    8. The ribosome finds the AUG start sequence on the messenger RNA.
    9. The ribosome finds a matching transfer RNA and lines it up alongside the messenger RNA strand.
    10. The ribosome finds a matching transfer RNA to the next 3 nucleotides.
    11. The ribosome removes the amino acid from the first transfer RNA and attaches it to the amino acid that just arrived.
    12. The ribosome continues finding transfer RNA molecules and joining amino acids until it reaches a stop codon (UAG, UAA, or UGA).
    13. The empty transfer RNA molecules leave the ribosome.
  8. If there is extra time, you may be able to have students switch roles and go through the process a second time in a new role.
  9. You may want to close the class with a discussion of how the classroom protein factory is different than the actual process taking place in nearly every cell in your body. For instance, the DNA molecule in the model only had 1 gene whereas real DNA molecules have thousands of genes. Also, RNA polymerase and ribosomes are just molecules and act like a machine in a factory, not like a thinking human being.

6. Protein Factory - Assessment

Assessment

  1. Ask students to summarize the job of the 5 players – DNA, messenger RNA, RNA polymerase, transfer RNA and the ribosome – in their own words.
  2. See the Comic Strip assessment idea for one creative way to gauge kids understanding of the protein synthesis process.

6. Protein Factory - Sources and Standards

Sources
This activity was put together from the bright ideas of several great teachers: Lori Lambertson of the Exploratorium Teacher Institute and Jim Youngblom of CSU Stanislaus.

Standards
Grade 8
Chemistry of Living Systems (Life Sciences)
6. Principles of chemistry underlie the functioning of biological systems. As a basis for understanding this concept:
c.     Students know that living organisms have many different kinds of molecules, including small ones, such as water and salt, and very large ones, such as carbohydrates, fats, proteins, and DNA.

Grade 9-12
Genetics
4.   Genes are a set of instructions encoded in the DNA sequence of each organism that specify the sequence of amino acids in proteins characteristic of that organism. As a basis for understanding this concept:
a.     Students know the general pathway by which ribosomes synthesize proteins, using tRNAs to translate genetic information in mRNA.
b.     Students know how to apply the genetic coding rules to predict the sequence of amino acids from a sequence of codons in RNA.
e.     Students know proteins can differ from one another in the number and sequence of amino acids.

7. DNA Fingerprinting

DNA adding tapeDNA adding tapeSummary
In this CSI activity, students solve a mystery using “DNA” taken from the scene of the crime. This write up describes how to collect a “DNA sample” (student invented DNA sequence on adding machine tape) from the culprit and from each person in the class, then run the DNA on a “gel” that covers the floor of the classroom, a hallway, or gymnasium. Naturally, the CSI aspect can become as elaborate as you wish by including additional “clues” such as fingerprints, a ransom note written in a specific type of ink, cloth fibers, eyewitness accounts and more. Since both DNA fingerprinting and paper chromatography (see Sources for lesson plans) rely on the same principles – separating molecules by size – a crime scene in which there is both a note written in a specific type of water-based ink as well as a DNA sample that may compared to the students’ DNA draws some interesting parallels conceptually between these two CSI techniques.

Objectives
Can explain what restriction enzymes do.
Can explain how gel electrophoresis works.
Can describe DNA fingerprinting methods.
Can discuss some of the considerations in evaluating DNA evidence in a crime.

Vocabulary
DNA replication
DNA polymerase
DNA fingerprinting
Restriction enzyme
Restriction fragment length polymorphisms
Short tandem repeats
Polymerase chain reaction
Gel electrophoresis

AttachmentSize
7dna_fingerprint.doc68 KB

7. DNA Fingerprinting - Logistics

Time
Day 1+: Investigating the crime scene (may take up to a week depending on the complexity of the evidence)
Day 2: Creating DNA samples and replicating DNA
Day 3: Running the “gel” and analyzing DNA fingerprint results

Grouping
Crime scene may be studied in teams or as a whole class. DNA samples are created and replicated individually. The gel is run and analyzed as a whole class.

Materials

  • Scissors
  • Adding machine tape (1 meter per person)
  • Meter sticks (or rulers)
  • Optional: Masking tape or blue painters tape to mark off a gel, loading wells, and lanes on the floor of the classroom, gym or hallway.
  • Optional: Additional materials to stage a crime scene. Be creative! For example, the kids walk into class to find the classroom pet kidnapped with a ransom note, a few human hairs (for a DNA sample) caught on the cage lid, and some fingerprints left behind. At my school, the gym teacher happily volunteered to be the culprit and all the teachers contributed an adding tape DNA sample for our analysis.

Setting
Classroom and possibly a hallway or gym to “run” your “gel”.

7. DNA Fingerprinting - Background

Teacher Background
The crux of this activity is the creation of a DNA sequence on a strip of adding tape, replication of the DNA, then using these DNA sequences to perform DNA fingerprinting.

DNA replicationDNA replicationThe base pairing rules help explain the process of DNA replication – how a cell makes an exact copy each strand of DNA just before it divides. First, an enzyme called helicase unzips the DNA down the middle of the ladder, in between the base pairs. Next, an enzyme called DNA polymerase reads one half of the strand, identifies a matching nucleotide, and builds a new partner strand. The process is complicated by the fact that DNA polymerase can only work in one direction along the sugar-phosphate backbone (remember, that the 2 backbones are oriented in opposite directions to one another). Thus, while DNA polymerase can easily run continuously along one strand, known as the “leading” strand, the other “lagging strand” must be assembled in a piecemeal fashion, one section at a time.

DNA fingerprinting is a technique used to distinguish between individuals of the same species using only samples of their DNA. Its invention by Sir Alec Jeffreys at the University of Leicester was announced in 1985.

DNA fingerprinting is used in forensic science, to match suspects to samples of blood, hair, saliva or semen. It has also led to several exonerations of formerly convicted suspects. It is also used in such applications as studying populations of wild animals, paternity testing, identifying dead bodies, and establishing the province or composition of foods. It has also been used to generate hypotheses on the pattern of the human diaspora in prehistoric times.

Two humans will have the vast majority of their DNA sequence in common. The traditional method of DNA fingerprinting uses restriction enzymes that cuts DNA at a specific sequence. Restriction enzymes work by recognizing a specific DNA sequence and cutting the DNA within this sequence. For instance, the restriction enzyme known as Sma1 looks for the sequence CCCGGG and cuts the DNA between the middle C and G. Other restriction enzymes make a staggered cut with some overhang on each end. For instance, the restriction enzyme EcoR1 looks for the sequence GAATTC and makes a staggered cut leaving what is known as a sticky end.

If designed correctly, a restriction enzyme can target a part of the genome that his highly variable from person to person such that some individuals’ DNA will be cut while others won’t, resulting in variable length DNA pieces. These differences are known as restriction fragment length polymorphisms. This technique is also often used to determine an individual’s genotype for a given gene – for instance, to test for the presence or absence of a mutation that confers a certain genetic disorder.

These DNA pieces may then be separated using gel electrophoresis. This method places the DNA sample in a well on one end of a sheet of agarose gel, similar to a thin layer of jello. An electric field is then applied to the gel. Since DNA is negatively charged, it is attracted to the positive end of the field and begins moving through the gel. The larger, longer fragments cannot travel as far through the gel matrix and get trapped near where the sample is loaded. The smaller, shorter fragments can wiggle their way through the matrix more easily and thus travel further. This results in a unique pattern of bands for each individual, depending on the DNA sequence.

Another common method of DNA fingerprinting exploits highly variable repeating sequences called short tandem repeats (STRs). Different people have different numbers of repeat units. For instance, the CSF gene contains the sequence AGAT repeated anywhere between 6 to 16 times. Two unrelated humans will be likely to have different numbers of this AGAT sequence.

While the variable number of repeats displayed at any single STR region will be shared by around 5 – 20% of individuals, if you look at several STR regions simultaneously, this method becomes incredibly powerful. The more STR regions that are tested in an individual the more discriminating the test becomes. In the U.S.A., there are 13 loci (DNA locations) that are currently used for discrimination. This has resulted in the ability to generate match probabilities of 1 in a quintillion (1 with 18 zeros after it) or more. Therefore, it is possible to establish a match that is extremely unlikely to have arisen by coincidence, except in the case of identical twins, who will have identical genetic profiles.

The process begins by extracting DNA from the cells in a sample of blood, saliva, semen, or other appropriate fluid or tissue. Next, each STR region is amplified using polymerase chain reaction (PCR) so that the initially tiny DNA sample is copied many times, creating a sufficiently large pool of DNA for analysis. Finally, the DNA fragments are then separated and detected using gel electrophoresis. Again, the shorter the sequence of repeats, the further the DNA fragment will travel through the gel.

Student Prerequisites
A solid understanding of DNA structure and base pairing rules.

7. DNA Fingerprinting - Getting Ready

Getting Ready

  1. Day 1 - Set up the crime scene. See Sources section for some great ideas for crimes that can be staged in a classroom and ideas for how to run a forensics unit.
  2. Day 2 - Cut adding tape into 1 meter long strips. Set out scissors and meter sticks.
  3. Day 3 – Tape out areas for the gels. All students can run their DNA on the same gel, or you can spread them out a little more by having groups of 5 students run their DNA on separate gels. For 5 students to run a gel, tape out a 100 inch (8.33 foot) x 60 inch (5 foot) rectangle. For all students to run their DNA on the same gel, you will need an area that is 100 inches long and wide enough for each student to have a minimum of 1 foot per person. The calculations are easiest if a single base pair DNA piece can travel 99 inches, 2 base pairs travel 98 inches, and so on. If your floor has small floor tiles, you can use those as your markers rather than inches.

7. DNA Fingerprinting - Lesson Plan

Lesson Plan
Day 1+ - Investigating the crime scene
If you set up a crime scene, make lots of observations of the crime scene. Start with all the kids outside the crime scene area, drawing pictures and writing down the things they notice. Finally, allow one student at a time enter the crime scene area wearing gloves to collect evidence. Evidence should be kept in plastic bags. Analyze any non-DNA evidence first. Dust for fingerprints. Collect hair and fiber samples. Perform paper chromatography on the ransom note and compare it against the pens in the possession of the various suspects. (See Sources section below for resources and lesson plans describing how to conduct these tests.)

Day 2 – Creating the DNA sequences and replicating DNA

  1. Each person should lay a meter stick down the middle of their strip of adding tape with the centimeter markings facing upward.
  2. Create a strand of DNA on the adding tape by writing a letter for a nucleic acid (A, T, C, or G) every centimeter along the top of the adding tape and writing the matching base below the meter stick. Remind students that they are creating their own individual DNA sequence and every person’s DNA is different, therefore they should independently make up their DNA sequence and not copy another student’s sequence.
  3. The first step of DNA replication uses scissors to represent the enzyme helicase. Helicase unzips the DNA down the middle of the DNA ladder, thus each student should cut their adding tape DNA down the middle between the bases, making sure there is white space on the paper both above and below the cut.
  4. Next, DNA polymerase finds the matching base and creates a new strand alongside the old strands. Your pencil is DNA polymerase and should follow along the half strands, filling in the matching bases. If you want, use a different colored pencil to create the new strand, that way you can tell the difference between the newly assembled strand and the original strand. Similarly, if you want, instruct students to fill in the matching bases continuously from left to right on the top “leading” strand but to fill in the matching bases on the bottom “lagging” strand 20 bases at a time from right to left. (Start at base #20, then match #19, #18, and so on until you hit #1. Then start at base #40, then match #39, #38, and so on until you hit #21.)
  5. Each person should end up with two exact copies of their DNA.


Day 3 – Running the “gel” and analyzing DNA fingerprint results

  1. Give students a quick overview of how DNA fingerprinting works:
    • collect the DNA sample
    • cut the sample with restriction enzymes
    • sort the pieces by length using gel electrophoresis
  2. Collect one copy of each students’ adding tape DNA. These may be pinned to a bulletin board and will form the class “DNA library”. Students should keep the other copy at their desks. Students can be told that you are “extracting a DNA sample” from each student to compare against the DNA of the culprit and other suspects. The “extraction process” used in this case results in paper strips of DNA rather than real DNA like the strawberry DNA extraction.Cutting DNA at sequence -AT-Cutting DNA at sequence -AT-
  3. Briefly describe what restriction enzymes are and how they work. The DNA sample the students kept will be cut using a restriction enzyme known at “AT”. Instruct students to read through the top row of their DNA. Any time they see the sequence AT (the complementary sequence below will read TA), they should cut the DNA in between the A and the T. On average, each student will make between 6 and 7 cuts although, depending on the sequence they created, some may make no cuts and some may make 20 or more.
  4. Next, students should measure the length of each DNA segment in centimeters and write this information on the back of each segment. Since each base pair was written 1 centimeter apart, the length of the DNA segment equals the number of base pairs on that segment.
  5. Line students up on the starting line of the gels. Explain how smaller segments will move farther. The rule is that each piece moves 100 inches minus the length of that piece. Thus a DNA segment only 1 base pair long can travel 99 inches, 2 base pairs travel 98 inches, and so on. An uncut DNA sample will not move at all and should stay on the staring line.
  6. Give students a few minutes to separate and sort their DNA pieces. When a given student is done, make sure they stand outside of the gel. It is easy to disturb DNA segments simply by walking past them.
  7. When all students have finished, stand back and look at the patterns made by the DNA segments. Some questions to ask include:
    • How many “bands” does each person have?
    • How far did the different segments move?
    • Did anyone have exactly the same pattern of bands as someone else? Why or why not?
    • Could this method be used to match a suspects DNA to a DNA sample taken from a crime scene? How?
    • How reliable is this method? Is it possible to have matching patterns but a different DNA sequence? Is it likely?
    • Should someone be convicted solely on DNA evidence? Should someone be released if DNA evidence shows they do not match the sample taken from the crime scene?
  8. Another direction to take this discussion is the ethics of maintaining a DNA library. DNA libraries generally only store information on STRs or restriction fragment length polymorphisms, not a person’s full genetic code. It is exceedingly useful in identifying offenders in situations where a DNA sample is collected from the scene of a crime. On the other hand, the existence of such a library may violate privacy rights. You could ask:
    • Now that you know how DNA fingerprinting works, how do you feel about the way I collected and saved a copy of your DNA in a DNA library?
    • Could a DNA library be useful in solving crimes?
    • How could a DNA library be abused or misused by the police or government?
    • Should governments maintain a DNA library? Why or why not?

7. DNA Fingerprinting - Assessment

Assessment

  1. Watch an episode of CSI that includes DNA fingerprinting data collection and evidence. Have students compare the techniques as seen on the show to the modeled version used in the classroom.

Going Further

  1. Have student run a gel in a virtual lab. The Genetic Science Learning Center at the University of Utah has a great online activity that allows you to load and run a gel
  2. If you have the equipment, teach your students to load and run a gel using any extracted DNA sample (see DNA Extraction lesson). Even if you don’t have gel boxes and fancy equipment, you can create your own functional gel boxes out of grocery store materials. The best write up for DNA extraction and running a gel “MacGyver style” can be found at BioTeach.

7. DNA Fingerprinting - Sources

Sources
If you are interested in creating a full-fledged CSI experience, an indispensable resource for teachers is the book, Mystery Festival, published by the Lawrence Hall of Science.

Other forensics science resources include:

  • Brian Bollone of Northpoint High School has made many of his teaching resources for his criminalistics and forensic science class available on the web.
  • Court TV has a wonderful series of mysteries to use in the classroom using a huge array of different techniques: DNA analysis, gunshot residue, pH testing, shoeprints, flame tests and more to solve the crimes.
  • DiscoverySchool.com has a large collection of forensic science resources for teachers.
  • Susan Seagraves created a fabulous “Whodunnit?” website with lesson plans for finger print analysis, chromatography, and mor.
  • The Shoder Education Foundation provides a comprehensive forensics resource for teachers including lesson plans, several mysteries, and resources.

Finally, for a great real world mystery to solve using DNA analysis among other techniques, go to the “Recovering the Romanovs” from DNA interactive by Cold Spring Harbor. It is quite simply, extraordinary.

Standards
Grade 7
Genetics
2. A typical cell of any organism contains genetic instructions that specify its traits. Those traits may be modified by environmental influences. As a basis for understanding this concept:
e.    Students know DNA (deoxyribonucleic acid) is the genetic material of living organisms and is located in the chromosomes of each cell.

Grades 9-12
Genetics
4. Genes are a set of instructions encoded in the DNA sequence of each organism that specify the sequence of amino acids in proteins characteristic of that organism. As a basis for understanding this concept:
c.     Students know how mutations in the DNA sequence of a gene may or may not affect the expression of the gene or the sequence of amino acids in an encoded protein.

5. The genetic composition of cells can be altered by incorporation of exogenous DNA into the cells. As a basis for understanding this concept:
a.    Students know the general structures and functions of DNA, RNA, and protein.
b.     Students know how to apply base-pairing rules to explain precise copying of DNA during semiconservative replication and transcription of information from DNA into mRNA.
d.    * Students know how basic DNA technology (restriction digestion by endonucleases, gel electrophoresis, ligation, and transformation) is used to construct recombinant DNA molecules.

8. Bird Beak Buffet

Summary
Inspired by observations of finches on the Galapagos Islands, Charles Darwin came up with an idea that is perhaps the most influential idea in all of science - natural selection. In this classic activity, students learn about natural selection by becoming birds foraging for food on an island (a large area of the schoolyard or classroom). The prey (beans) vary in their coloration such that some blend into the environment better than others. The birds vary in the type of beak they have (plastic forks, spoons and knives). Each season, any prey that survives has a baby bean the same color as the parent. In addition, the most successful birds has a baby with the same beak trait while the least successful birds die (and are reincarnated as the babies of the successful birds). Over several generations, the bird and bean populations shift depending on the environment. Well camouflaged beans survive and reproduce. Birds with beaks that can easily capture beans survive and reproduce. In this way, students model natural selection in 2 species and get a very good idea of how natural selection works.

Objectives
Can explain what natural selection is and the conditions necessary for it to occur.
Can discuss changes in a population in the context of natural selection.
Can use terms such as natural selection, evolution, and adaptation scientifically.
Can organize data in a table and graph.
Can graph changes in a population over time.

Vocabulary
Trait
Population
Natural selection
Adaptation
Fitness
Evolution
Charles Darwin

AttachmentSize
8bird_beak.doc69 KB
bird_beak_student.doc60 KB
bird_beak_data.doc67.5 KB

8. Bird Beak Buffet - Logistics

Time
15-20 minutes introduction
45-50 minutes activity (The lesson plan is written so that the activity is introduced on one day and actually done the following day. It is also possible to introduce the activity and go through one or two years on the first day and complete the activity on the following day.)
15-20 minutes organize and summarize data
30+ minutes discussion

Grouping
Each student is a bird foraging in the same feeding ground. At the end of each year, students gather in a group of similar-beaked birds to enter their foraging results on a clipboard. The introduction and final discussion occurs as a whole class in a classroom.

** If working as a whole class in a single feeding ground is too chaotic for your students, then this activity may be done in smaller groups of 3 or 6. Each group will get their own 1 meter square plot of ground or even a cafeteria tray on a table in the classroom to forage in. Each group starts with 1 or 2 representatives of each of the 3 beak types in the group and 100 beans of each color in the feeding ground. After each season, they should summarize their data and add new beans to their feeding ground. The bird that eats the most will reproduce and the bird that eats the least will die and get reincarnated.**

Materials

  • 1 pound of red beans
  • 1 pound of black beans (of a similar size and shape as the other beans)
  • 1 pound of white beans (of a similar size and shape as the other beans)
  • 25 plastic forks
  • 25 plastic spoons
  • 25 plastic knives
  • 30 paper cups
  • 1 stopwatch
  • 1 whistle
  • broom and dustpan for cleanup
  • 1 copy of the Bird Beak student handout for each student
  • 3 copies of the Bird Beak data tables
  • 4 clipboards with a pencil/pen tied to each
  • Optional: masking tape or string to designate the borders of the feeding ground

Setting
The activity takes place in an 80 square foot (9x9 foot square) feeding ground located in the classroom, on a concrete school yard or in a grassy field. The introduction and post-activity discussion takes place in the classroom.

8. Bird Beak Buffet - Background

Teacher Background
Perhaps the most important idea in all of biology, or perhaps all of science, is the idea of evolution through natural selection. This idea by Charles Darwin provides the foundation of all of current scientific thinking in life science.

What is evolution? Quite simply, evolution is descent with modification. This includes both the idea that the frequency of a gene will change in a population over time as environmental conditions change and also the idea that new species descend from common ancestors over many generations. Ultimately, evolution can explain the vast diversity of life on this planet and the idea that all life on Earth shares a common ancestor.

Although there are many mechanisms for organisms to change over time, the most important of these is natural selection. It works in this way:

  • There is variation in a population. Different individuals have different traits.
  • There is heredity. Traits can be passed on from parent to offspring through our genes.
  • There is competition (sometime referred to as differential survival and reproduction) so that some individuals survive and reproduce more than others.
  • The end result is natural selection – the individuals with the traits that best fit the environment are most likely to survive, reproduce, and pass on their traits to the next generation. In this way, future generations, when viewed at the level of an entire population, will have more advantageous traits and fewer disadvantageous traits compared to their parents.

There are many other mechanisms for evolutionary change besides natural selection:

  • Artificial selection is a common practice for humans to breed together plants or animals with the most advantageous traits (the sweetest tomato, the most loyal dog, the fastest horse, etc.). Thus, future generations will have more of these traits.
  • Mutation can affect the distribution of traits by introducing a new trait to a population.
  • Migration can rapidly change the overall distribution of traits in a population when a group of organisms with different traits enters a new area. For example, a group of small beaked finches is blown over to an island with primarily large beaked finches by a hurricane.
  • Genetic drift can affect a population through a random chance event – like a hurricane or human activity – randomly destroying organisms with one trait but not another. For instance, when a new house is constructed in a neighborhood with both red and brown ground squirrels, it accidentally bulldozes the nest of the largest red ground squirrel family. Suddenly, brown ground squirrels predominate.

A final important term that is often misused by students is adaptation.  An adaptation is a trait that is very well suited to a given environment that has, through natural selection, increased in the population over many generations. Students often talk and think about adaptation as if an organism can try to adapt or is able to get what it needs. In neither case are they correct. An organism can’t get the genes it needs to survive by “trying”; it either has the genes or not. Similarly, natural selection doesn’t have a goal in mind and cannot give a creature what it “needs”; either the genes are there in the population or not.

In this activity, students come to understand natural selection, evolution and adaptation through modeling changes in 2 populations – a population of birds with different beak traits and a population of beans with different color traits.

Student Prerequisites
None required although an understanding of variation in traits is helpful (see Human Traits activity or Snail Variations project).

8. Bird Beak Buffet - Getting Ready

Getting Ready

  1. Purchase beans, cups and plastic utensils.
  2. Make copies of the Bird Beak student handout for each student.
  3. Make copies of the Bird Beak data tables. For each class that will do the activity you should have 3 copies of “_____-Billed Bird Population Data” and 1 copies of “Bean Population Data”. Attach these data tables to the 4 clipboards.
  4. On the 3 “_____-Billed Bird Population Data” clipboards, fill in the blanks with “Fork”, “Spoon”, and “Blade”.
  5. For each class or students, count out 100 red, 100 black, and 100 white beans and mix them together in a ziplock bag or cup.
  6. Optional: mark the feeding ground boundaries with tape or string.

8. Bird Beak Buffet - Lesson Plan

Lesson Plan
Day 1 - Introduction

  1. Open class with a discussion of what human traits might help a person be more successful (Is it an advantage to be tall? Is it an advantage in America to be blond haired and blue eyed? How about in another country like Africa or Asia?) Leave the interpretation of “more successful” open and somewhat vague. If this seems to controversial for your group of students, then discuss variation in cat or dog traits and what might help a pet survive better (Is it an advantage for a cat to be shy? Is it an advantage for a dog to be friendly?).
  2. Lead the discussion towards thinking about what “more successful” really means. Does that mean being more popular or making more money or more likely to live happily ever after? In scientific terms, what matters in the long run is whether you survive, find a mate, and reproduce, passing on your genes to the next generation.
  3. Introduce the activity. Pass out the handout and describe the rules.
  4. Check that students understand that all the birds are of the same species but have different beak traits. Similarly, all the beans are of the same species but have different color traits.
  5. Check that students understand that the birds that eat the most food will have a baby with a similar beak and that the birds that eat the least will die. Similarly, surviving beans (those not eaten) will have one baby with the same color trait.
  6. Finally discuss the data collection that occurs after each round. Each student is responsible for counting the number of each type of bean they eat and entering their data on the bird population data clipboards. Once all the bird population data has been gathered, then a volunteer from each group will report their data on the bean population data clipboard. 
  7. If data will also be collected in lab notebooks, have students copy or paste the data tables and graphs into their notebooks.


Day 2 – Bird Beak Buffet

  1. Distribute a cup to each student. Next, give each student a plastic utensil.
  2. Quickly go over the rules before heading out to the feeding ground. Make sure you bring clipboards, beans, a stopwatch, and a whistle.
  3. Place the 4 data clipboards in different locations near the feeding ground.
  4. Have students stand on the edge of the feeding ground. Sprinkle the mixed beans (100 of each type) into the feeding ground.
  5. Blow the whistle and give students 20 seconds to “eat” as many beans as possible. Look out for students that cheat (have cups touching the ground, interfere with other students, etc.) and dump out the contents of their cups or eliminate them from the game. Blow the whistle again to signal the end of the year.
  6. Each student should go to the clipboard for their beak type, count the number of beans of each type they ate, and enter that information in the data table.
  7. Each group should calculate the grand total number of beans of each type that were eaten by their group (the bottom row of the table).
  8. One volunteer from that group can bring that information to the bean population data clipboard and enter their groups’ information. The volunteers can then help to complete the bean data table and count out the proper number of beans to add to the feeding ground.
  9. While the volunteers are entering bean population data, the rest of the students should help to sort their beans by color and return them to the stockpiles.
  10. Finally, have students line up by the total number of beans they ate. Have the 5 students that ate the fewest beans act out a grisly death. (Acting out the deaths helps students realize that they are actually dying and entering the game as a new bird with new traits, not just trading in one tool for another.) Confiscate their utensils. Give them new beaks that match the beaks of the 5 students that ate the most beans.
  11. Have a student enter this information (the number of birds that died and number of babies born) on the bird population data clipboards.
  12. Repeat steps 5-11 for each of the next 3 years of the game for a total of 4 rounds.
  13. Collect the clipboards, cups and utensils. Sweep up any remaining beans.

Day 3 – Organize, graph and discuss data

  1. Create data tables on the board (or make and overhead copy) similar to the ones on the second page of the Bird Beak Student handouts.
  2. Use the information from the clipboards to fill in the summary table. Have students fill in their tables as well.
  3. Have students graph the data for each population (red beans, white beans, black beans, fork-bills, spoon-bills, blade-bills) with years 1-5 on the x axis and the number of organisms at the start of a year on the y axis. The graphing may be done:
    • individually in their lab notebooks
    • groups of 3 can each graph one bird and one bean and analyze graphs as a group
    • a group of students can create large poster sized graph for one of the populations to display around the room.
  4. Discuss the graphs. Notice patterns such as one population going up while another goes down. See if the population is growing steadily or exponentially.
  5. Discuss the reasons why one population did well while another did poorly. Is there a different scenario in which a different bird or bean would do best?
  6. At this point it is possible to formally address some of the vocabulary.
    • Discuss natural selection – the process by which organisms with traits that best suit the environment are most likely to survive, reproduce, and pass on their genes to the next generation. In this activity, the bean that had the best camouflage and that was the hardest to catch survived, reproduced, and passed on their genes.
    • Discuss evolution – descent with modification, most often as the result of natural selection. In this activity, we started with the same number of beans of each type but ended up with the population skewed towards the beans with the best suited traits.
    • Discuss adaptation – a trait that is very well suited to a given environment that has, through natural selection, increased in the population over many generations. In this case, a particular color of bean could be considered an adaptation since it increased in the population through natural selection.
  7. Describe Charles Darwin’s adventures on the Beagle and how his observations (particularly of the finches on the Galapagos Islands) led him to propose the idea of natural selection.
  8. Begin the process of busting the misconceptions that students have about evolution. See the Understanding Evolution website for a fabulous overview of the common misconceptions students have and responses to those misconceptions.
  9. Finally, return to the discussion you used to open this activity – what human traits might help someone be more successful – and revisit those issues in the light of what your students now know about natural selection and evolution. In particular, you can discuss whether and how natural selection has worked and is still working on the human species.

8. Bird Beak Buffet - Assessment

Assessment

  1. Collect the students’ graphs and responses to the conclusion questions.
  2. Before the activity, have students write a short essay about “what is evolution and how does it work?” These may be collected to give you as the teacher a sense of what their initial understanding may be. After the activity and discussion, have students revise their essay to reflect what they now know about evolution.

Going Further

  1. Conduct a deeper investigation of the Galapagos finches. There are many resources that you can use to help you in this quest. First of all, read the Pulitzer Prize winning book The Beak of the Finch, by Jonathan Weiner. The book flips back and forth between Darwin’s original studies and the modern day work of Peter and Rosemary Grant. The Grants have spent over 20 consecutive years studying the Galapagos finches. They recognize each and every finch living on the island and know the family relationships between every individual bird. Several lesson plans for teachers have been developed from their work:
    • The PBS evolution site provides a downloadable pdf file with several graphs showing changes in finch beaks over time. One of PBS's online courses addresses some of the questions raised by the data and may be appropriate to use directly with high school students.
    • Teachers Domain has adapted the data from the PBS evolution site slightly to create a lesson plan for teachers with discussion questions about the data
    • There is a good 1995 video of the Grants’ work called “What Darwin Never Saw”, produced by PBS for “The New Explorer” series with Bill Kurtis. Several teacher groups have created lesson plans that follow the video including one from ENSI web and one from the Chicago Academy of Sciences.
    • Finally, for the most advanced students, go straight to some original data and look for patterns and correlations. Prentice Hall has created a lesson plan suitable for AP Biology and college level courses looking at the effect of drought on one species of finch
  2. Another hands-on approach to further investigations of bird beaks is provided in this lesson from TERC. Students use a spring scale to measure the force required to crack a nut with pliers that represent different types of bird beaks.
  3. Finally, there are several videos that provide excellent information on evolution and Charles Darwin.
    • PBS produced a fabulous 7 episode series on evolution. There’s excellent snippets on the evolution of drug resistance in HIV, summaries of Darwin’s work, discussions of evolution and religion, and more. Unfortunately, it is expensive, at $100 for the DVD set alone or $130 for the educators’ set with curriculum.
    • As part of the PBS evolution series, there are several quicktime movie clips that can be viewed over the internet and an associated teacher's curriculum guide with activites and lesson ideas.

8. Bird Beak Buffet - Sources

Sources

The Bird Beak Buffet activity is a classic in the teaching of natural selection and evolution. There are hundreds of write ups out there with all sorts of different variations. I first learned about the activity from Kimberly Tanner, currently faculty at San Francisco State University. I found a box of materials to borrow from Chris Giorni of Tree Frog Treks. Then I participated in a workshop with Karen Kalamuck of the Exploratorium Teachers’ Institute.

There are many variations of this activity on the web from many different organizations:

For background resources on better understanding evolution, nothing beats the Understanding Evolution site from the UC Museum of Paleontology. There you can find everything from evolution 101 to scientific articles to student misconceptions to lesson plans. It’s a one-stop resource for all a teachers’ needs.

Finally, if your school district, administrators or parents opposes the teaching of evolution, see the National Center for Science Education for articles and resources that can help you justify what you are doing in your classroom.

Standards
Grade 7
3. Biological evolution accounts for the diversity of species developed through gradual processes over many generations. As a basis for understanding this concept:
a. Students know both genetic variation and environmental factors are causes of evolution and diversity of organisms.
b. Students know the reasoning used by Charles Darwin in reaching his conclusion that natural selection is the mechanism of evolution.
e. Students know that extinction of a species occurs when the environment changes and the adaptive characteristics of a species are insufficient for its survival.

Grade 9-12
7.   The frequency of an allele in a gene pool of a population depends on many factors and may be stable or unstable over time. As a basis for understanding this concept:
a. Students know why natural selection acts on the phenotype rather than the genotype of an organism.
d. Students know variation within a species increases the likelihood that at least some members of a species will survive under changed environmental conditions.

8. Evolution is the result of genetic changes that occur in constantly changing environments. As a basis for understanding this concept:
a. Students know how natural selection determines the differential survival of groups of organisms.
b. Students know a great diversity of species increases the chance that at least some organisms survive major changes in the environment.

Assessment - Comic Strip

Protein synthesis comic strip: Created by teachers from the Science STARTS/Delta Sierra Science Program summer instituteProtein synthesis comic strip: Created by teachers from the Science STARTS/Delta Sierra Science Program summer institute

 

Summary
Let your creative juices flow. The process of translating nucleic acids into amino acids becomes a tale of suspense, drama and adventure as you come up with a Marvel Comics style adventure story that is an analogy for protein synthesis. Draw comparisons between DNA and a secret message written in code. Compare ribosomes to factories churning out products. Students will surprise you with the crazy analogies they can come up with and the elegant stories they can spin.

Objectives
Reinforce and assess students’ understanding of the central dogma of molecular biology.

Vocabulary
DNA
Genetic code
Nucleotide
Base pair
RNA polymerase
Messenger RNA
Transfer RNA
Amino acid
Ribosome

AttachmentSize
Assess_comic.doc41 KB

Comic Strip - Logistics

Time
30 min to introduce the activity. 1-3 hours to complete and present the comic strips.

Grouping
Individual

Materials

  • White copy paper
  • Colored pencils
  • Optional: handouts or overhead specifying the concepts that must be included

Setting
Classroom

Comic Strip - Getting Ready

Teacher Background
See background information from Protein Factory lesson.

Student Prerequisites
Good understanding of DNA structure (see DNA Models lesson) and protein synthesis (see Protein Factory lesson).

Getting Ready

  1. Set out paper and colored pencils
  2. Optional: make copies of concepts

Comic Strip - Lesson Plan

Lesson Plan

  1. Review the idea of transcription and translation. As you do, write down key concepts (see table below) in a column on the side of the board.
  2. Protein synthesis key concepts:
    • DNA is located in the nucleus of the cell.
    • The sequence of DNA nucleotides forms the genetic code.
    • RNA polymerase separates the 2 strands of DNA and then matches an RNA nucleotide to each DNA nucleotide.
    • This chain of RNA nucleotides forms a molecule of messenger RNA.
    • The messenger RNA leaves the nucleus.
    • A ribosome assembles around the messenger RNA
    • The ribosome reads the sequence of codons in the messenger RNA and matches a transfer RNA molecule to each codon.
    • The ribosome assembles the amino acids brought by the transfer RNA into a chain.
    • The finished chain of amino acids is a protein.

  3. Once you have elicited the major steps of transcription/translation, cross out or underline the vocabulary words. For example:
    • DNA is located in the nucleus of the cell.”
    • “The sequence of DNA nucleotides forms the genetic code.”
  4. Ask students to be creative and brainstorm other words or ideas that might fit in the place of the crossed out/underlined words. For example, instead of “DNA is located in the nucleus of the cell” you might say
    • The mayor is located in the town hall of the city.”
    • A beautiful princess is located in the highest tower of the castle.”
    • The Pirate King is located on his pirate ship in the middle of the Black Sea.”
  5. Use this brainstorming strategy for perhaps 2 or 3 key concepts then begin tying the ideas together to create a non-science storyline that parallels the protein synthesis process. Perhaps the princess is sending a secret message to her knight in shining armor to build a device to rescue her. Or maybe the Pirate King is sending secret orders to his henchmen on land to build a weapon.
  6. Once students get the idea, give them an overview of the project: Create a comic strip that is an analogy for the protein synthesis process. Below each panel of the comic strip, write down the translation of your story in science speak (the key concepts listed above). Begin by outlining the entire story side by side with the science speak key concepts. Only after the story is outlined should you begin illustrating.

6. Comic Strip - Sources and Standards

Sources
The inspiration for this assessment activity is the book The Cartoon Guide to Genetics by Larry Gonick and Mark Wheelis. It’s a wonderful textbook alternative that teaches genetics in a very entertaining, humorous way.

Standards
Grade 7
Genetics
2. A typical cell of any organism contains genetic instructions that specify its traits. Those traits may be modified by environmental influences. As a basis for understanding this concept:
e.    Students know DNA (deoxyribonucleic acid) is the genetic material of living organisms and is located in the chromosomes of each cell.

Grades 9-12
Cell Biology
1. The fundamental life processes of plants and animals depend on a variety of chemical reactions that occur in specialized areas of the organism's cells. As a basis for understanding this concept:
d.     Students know the central dogma of molecular biology outlines the flow of information from transcription of ribonucleic acid (RNA) in the nucleus to translation of proteins on ribosomes in the cytoplasm.

Genetics
4. Genes are a set of instructions encoded in the DNA sequence of each organism that specify the sequence of amino acids in proteins characteristic of that organism. As a basis for understanding this concept:
a.     Students know the general pathway by which ribosomes synthesize proteins, using tRNAs to translate genetic information in mRNA.
b.     Students know how to apply the genetic coding rules to predict the sequence of amino acids from a sequence of codons in RNA.
e.     Students know proteins can differ from one another in the number and sequence of amino acids.

Assessment - Real World Problems

Summary
The following are a series of real world genetics problems that relate to the genetic disorders cystic fibrosis and sickle cell anemia. They may be used to give students practice with Mendelian genetics and molecular biology or at the end of the unit to assess their understanding of various concepts.

Objectives
Reinforce and assess students understanding of real world genetics issues.

AttachmentSize
Assess_Real_World.doc42 KB

Real World - Cyctic Fibrosis

Cystic Fibrosis
Cycstic fibrosis breathing apparatusCycstic fibrosis breathing apparatusCystic fibrosis is a genetic disease that affects many different parts of the body. There are approximately 30,000 Americans with cystic fibrosis. The most serious problem is the production of extremely thick, sticky mucus that clogs up the bronchial tubes in the lungs and the passageways in the pancreas (remember, the pancreas makes digestive juices that help break down food). This causes malnutrition, diabetes, lung infections, and difficulty getting enough oxygen to the body. Most people with cystic fibrosis die in their 20s or 30s from lung failure.

Cystic fibrosis is caused by a mutation in the cystic fibrosis gene. This gene provides the code for a protein that helps produce digestive juices and mucus.

  • Using what you know about DNA, what does it mean for there to be “a mutation in the cystic fibrosis gene”?
  • The most common mutation in the cystic fibrosis gene is the deletion of 3 nucleic acids. In other words, in the mutated form of the gene, 3 nucleic acids in a row are missing. How would this mutation affect the protein that would normally be produced?

CFTR geneCFTR geneCystic fibrosis is a recessive genetic disease. The normal allele can be represented by “G” and the mutant allele can be represented by “g”.

  • If you have the cystic fibrosis disease, what is your genotype? _____
  • Approximately one in 25 Americans has a mutation in the cystic fibrosis gene. Does this mean that all of those people will have the disease? Explain your answer by describing the possible genotypes of people that carry a mutant allele.

Cindy and Jonathan were married one year ago and are thinking of starting a family. Neither has cystic fibrosis. However, Cindy’s younger sister is very sick with cystic fibrosis. This has made Cindy and Jonathan worried that a baby they have together may be born with cystic fibrosis.

  • Cindy’s parents do not have cystic fibrosis. Knowing that Cindy’s sister has the disease, what must Cindy’s parents’ genotypes be? ____ (Clearly explain how you figured out their genotype.
  • What kinds of kids could Cindy’s parents have? Draw a Punnett Square to help you answer the questions below.

What are the chances that one of their kids is GG? ________%
What are the chances that one of their kids is Gg? ________%
What are the chances that one of their kids is gg? ________%

Cindy and Jonathan decide to get genetic testing to see whether either of them carries a mutant cystic fibrosis gene. Remember, Cindy and Jonathan do not have cystic fibrosis.

  • The results come back saying that Cindy is heterozygous. What is her genotype? _____
  • Jonathan’s results say that he is homozygous. What is his genotype? _____
  • What are the chances that Cindy’s and Jonathan’s kids will have cystic fibrosis. Explain completely how you know. Use a Punnett square if that helps you show the possibilities.

Real World - Sickle Cell Anemia

Sickle Cell Anemia
Sickle-shaped red blood cellsSickle-shaped red blood cellsSickle cell disease is a disorder that affects the red blood cells. Red blood cells use a protein called hemoglobin to transport oxygen from the lungs to the rest of the body. Normally, red blood cells are round and flexible so they can travel freely through the narrow blood vessels.

Patients with sickle cell disease have a mutation in a gene that codes for part of the hemoglobin protein. As a result, hemoglobin does not form properly, causing red blood cells to be oddly shaped. These irregularly shaped cells get stuck in the blood vessels and are unable to transport oxygen properly, causing pain, frequent infections, and damage to the organs. Patients with sickle cell disease only survive to be 20 to 30 years old. About 1 in 500 babies born in America has the disease.

The normal hemoglobin nucleic acid sequence looks like:
T A C C A C G T G G A C T G A G G A C T C
A T G G T G C A C C T G A C T C C T G A G

Use the genetic code below to decode the top strand of the DNA.

Genetic CodeGenetic Code

  • The messenger RNA would read:
  • The protein message would read:

The mutant form of the hemoglobin gene is shown below with the mutation highlighted:
T A C C A C G T G G A C T G A G G A C A C
A T G G T G C A C C T G A C T C C T G T G

  • Describe the difference between mutant allele and the normal allele.
  • How would this mutation affect the hemoglobin protein that would normally be produced? In your answer, explain exactly what would happen to the amino acid sequence and how that might affect hemoglobin’s ability to do its job.

Sickle cell disease is a recessive genetic disease. The normal hemoglobin allele can be represented by “H” and the mutant allele can be represented by “h”.

  • If you have sickle cell disease, what is your genotype? _____
  • If you do not have sickle cell disease, what could your genotype be? _____ or _____

Jack and Jill were married one year ago and are thinking of starting a family. Neither has sickle cell disease. However, Jack’s younger sister is very sick with sickle cell disease. This has made Jack and Jill worried that a baby they have together may be born with sickle cell disease. Jack and Jill decide to get genetic testing to see whether either of them has a mutant hemoglobin gene. The results come back saying that both Jack and Jill are both Hh.

  • What are the chances that their kids will have sickle cell disease. Explain completely how you know. Use a Punnett square to help you show the possibilities.
  • In general, is having sickle cell disease an advantageous trait to have?
  • In terms of natural selection, what should happen to the prevalence of sickle cell disease in a population over several generations?
  • Should the prevalence of the mutant form of the hemoglobin gene (h) increase or decrease over time?

Sickle cell disease is most common in people of African, Indian or Middle Eastern descent. Africa, India and the Middle East all have a big problem with another disease - malaria. If you get malaria, you become extremely sick with a high fever, vomiting, convulsions and possible organ failure. Infants and children are particularly vulnerable. Almost 1 million children die from malaria each year.

Interestingly, people that only have one copy of the mutant hemoglobin gene are more resistant to malaria. If infected, they become only slightly sick (with symptoms more like the common cold) and children that are heterozygous rarely die from malaria!

  • What does it mean for someone to be “heterozygous”?
  • In areas where there is a lot of malaria, is being heterozygous for the sickle cell gene an advantageous trait?
  • In terms of natural selection, what should happen to the prevalence of the mutant form of the hemoglobin gene (h) over time in areas with a big malaria problem?

Project - Dragon Genetics

Summary
In this long term computer based simulation, students play with a fabulous FREE software program called Biologica developed by the Concord Consortium. It offers an in depth, virtual experience exploring Mendelian inheritance patterns in dragons. Activities increase in complexity from initial modules introducing dragons and their chromosomes to later activities that require problem solving skills and the integration of many levels of prior knowledge. In the program, you can manipulate dragon chromosomes, breed dragons, explore pedigrees, and more. There are fantastic puzzles along the way: Which gametes should you select to breed a purple, fire breathing, boy dragon? What happens if you change the DNA sequence? Can you figure out the genotype of invisible dragon parents from the phenotypes of their offspring?

Objectives
Can explain and use the relationship between genotype and phenotype to explain inheritance patterns.
Can take genotype information from 2 parents, model the creation of gametes by independent assortment, and use those gametes to create offspring.
Can explain the relationship between DNA, genes, and chromosomes.
Can explain how the inheritance of sex chromosomes contribute to an individual’s sex and to X-linked traits.
Can use Punnett squares to predict the possible allele combinations in the offspring given the genotypes of the parents.
Can understand the role of mutations in creating variation in phenotypes.

Vocabulary
Phenotype
Genotype
Gene
Allele
Chromosome
Dominant
Recessive
Incomplete dominance
Homozygous
Heterozygous
X linkage
Y chromosome
Meiosis
Gamete
Zygote
Punnett square
Monohybrid cross
Pedigree

AttachmentSize
Proj_Dragon_Genetics.doc49.5 KB

Dragon Genetics - Logistics

Time
Students may spend anywhere between 1-8 hours playing with dragon genetics. There are 12 activities total. Each activity takes students between 20-50 minutes to complete depending on how quickly the child works. The full sequence is as follows:

  • Introduction – What do dragons look like and why?
  • Rules – What’s the relationship between genotype and phenotype?
  • Meiosis – Why don’t family members look the same?
  • Horns Dilemma – Can 2 horned parents have a hornless baby?
  • Monohybrid – What can you learn from pedigrees?
  • X Linkage – What happens if a gene is part of the X chromosome?
  • Mutations – A unicorn dragon! What happened?
  • Mutations 2 – What happens if you change the DNA?
  • Dihybrid cross – How likely is it for 2 traits to be inherited together?
  • Scales – How do you study the inheritance of a new mutation?
  • Invisible dragons – Dan you determine the genotype of parent dragons just by looking at the phenotypes of the offspring?
  • Plates – How are plates inherited?

It is not necessary or even recommended to complete every activity. My middle school students completed the abbreviated sequence below in 4 class periods. Students who finished early could continue on to the other activities.

  • Introduction – What do dragons look like and why?
  • Rules – What’s the relationship between genotype and phenotype?
  • Meiosis – Why don’t family members look the same?
  • Monohybrid – What can you learn from pedigrees?
  • Mutations – A unicorn dragon! What happened?

Grouping
Individual although students working in pairs on the same computer is also fine.

Materials
Computer lab with at least one computer for every 2 students
Optional: For later modules, you may want to provide or have students create a paper “Dragon Genetics Rules” handout listing each of the traits and a phenotype to genotype translation (HH = horns, Hh = horns, hh = no horns).

Setting
Computer lab.

Dragon Genetics - Background

Teacher Background
My middle school students absolutely adored working on the program and begged me for more time to spend in the computer lab on it. The logical reasoning skills required in the advanced activities is quite sophisticated so use caution when requiring this program of students in 6th grade or below.

The Concord Consortium has created an excellent, downloadable teacher guide so see their materials for additional teacher background information. For questions about the software itself, see the Frequently Asked Questions area.

Student Prerequisites
None required although the first activity (Introduction) contains a whole lot of vocabulary. Therefore, I preferred introducing Dragon Genetics after students had been introduced to genes, alleles, and simple dominance (see Making Babies Lab).

Dragon Genetics - Lesson Plan

Getting Ready

  1. Download the Biologica program to each computer. Follow the step by step directions given on the Concord Consortium website.

Lesson Plan

  1. Open the Pedagogica program.
  2. Open the Biologica folder. 
  3. Begin working on activity #1 - Introduction. From here, it is very self explanatory. Students can work at their own pace. Students who finish early can work on some of the optional activities.

Dragon Genetics - Assessment

Assessment

  1. Invisible Dragons is an excellent alternative assessment tool that requires students use all their previous skills to solve a puzzle. I used the Invisible Dragons as an extra credit challenge for the students who wanted to try.

Dragon Genetics - Standards

Standards
Grade 7
Genetics
2. A typical cell of any organism contains genetic instructions that specify its traits. Those traits may be modified by environmental influences. As a basis for understanding this concept:
b.     Students know sexual reproduction produces offspring that inherit half their genes from each parent.
c.     Students know an inherited trait can be determined by one or more genes.
d.     Students know plant and animal cells contain many thousands of different genes and typically have two copies of every gene. The two copies (or alleles) of the gene may or may not be identical, and one may be dominant in determining the phenotype while the other is recessive.
e.    Students know  DNA (deoxyribonucleic acid) is the genetic material of living organisms and is located in the chromosomes of each cell.

Grades 9-12
Genetics
2. Mutation and sexual reproduction lead to genetic variation in a population. As a basis for understanding this concept:
a.     Students know meiosis is an early step in sexual reproduction in which the pairs of chromosomes separate and segregate randomly during cell division to produce gametes containing one chromosome of each type.
b.     Students know only certain cells in a multicellular organism undergo meiosis.
c.     Students know how random chromosome segregation explains the probability that a particular allele will be in a gamete.
d.     Students know new combinations of alleles may be generated in a zygote through the fusion of male and female gametes (fertilization).
e.     Students know why approximately half of an individual's DNA sequence comes from each parent.
f.     Students know the role of chromosomes in determining an individual's sex.
g.     Students know how to predict possible combinations of alleles in a zygote from the genetic makeup of the parents.

3.   A multicellular organism develops from a single zygote, and its phenotype depends on its genotype, which is established at fertilization. As a basis for understanding this concept:
a.     Students know how to predict the probable outcome of phenotypes in a genetic cross from the genotypes of the parents and mode of inheritance (autosomal or X-linked, dominant or recessive).
b.     Students know the genetic basis for Mendel's laws of segregation and independent assortment.
c.     * Students know how to predict the probable mode of inheritance from a pedigree diagram showing phenotypes.

Project - Snail Variations

Summary
Variation in a population is the raw material on which natural selection works. How do scientists measure and quantify variation in traits? We use garden snails as a model organism in order to describe and measure several different traits. Groups are given a small population of snails and must devise an objective way to measure a trait of their choosing (length, mass, speed, color intensity, stripes, withdrawal reflex reaction time, number of pennies it can carry, etc.). There are many ways to extend this activity. For instance, scientific protocols may be traded between groups, hypotheses may be made concerning what individuals will survive better in different environments, and snails may be tagged and released into one or more environments and the populations monitored over time. A long term open-ended project such as this provides a natural extension and assessment opportunity for both evolution and ecology concepts.

Objectives

Can make observations in an objective, quantifiable manner.
Can select and use tools to collect data.
Can use tables and graphs to represent data and identify patterns in data.
Can describe the role of variation in a population in natural selection and evolution.

Vocabulary

Traits
Variation
Population
Natural selection
Evolution
Objective
Subjective
Quantify
Histogram

AttachmentSize
Proj_Snail_Variations.doc47 KB

Snail Variations - Logistics

Time
50 minutes to measure, quantify, and discuss variation in snail traits. The extension projects described in the Going Further section may last several months.

Grouping
Teams of 3-4 students.

Materials
For each group of 3-4 students you need:

  • 1 plastic shoebox
  • wet paper towels
  • vegetables
  • 4-6 snails
  • 2 hand lenses
  • 1-2 clear rulers
  • 1 stop watch
  • Optional: 2 bottles of nail polish in different colors

Other supplies you may want on hand for groups to share:

  • scale or balance
  • Petri dishes
  • pennies or washers for students to measure how much a snail can carry
  • masking tape
  • paint color samples from a local hardware store in all shades of beige, brown and black
  • different textured surfaces (copy paper, mirrors, construction paper, overheads, sand paper, aluminum foil etc.)
  • pH paper

Setting
Initial measurement of snail traits can be done in the classroom. Extension projects should be done in a schoolyard, garden, creek, park or other local outdoor area that has a resident snail population – ideally, this is the location where the snails were collected.

Snail Variations - Background

Teacher Background
Natural selection and evolution are core ideas in biology and, in fact, all of science. Natural selection can briefly be described the process by which those individuals whose traits best fit their environment are most likely to survive, reproduce, and pass their genes on to the next generation. One of the critical “raw ingredients” of natural selection is variation in a population. All natural populations (groups of organisms of the same species) vary in their traits based on the interplay between genetics and environmental factors.

This activity uses the common garden snail (Helix aspersa) to measure variations in a population. These animals are garden pests found throughout North America and are readily captured from around most neighborhoods in California. I generally pay my neighbor’s kids 5¢ a snail and end up with upwards of 40 snails in less than an hour.

Snails are incredibly easy to keep in the classroom. They can survive in the classroom almost indefinitely with regular feeding and cleaning. Keep snails in a plastic shoebox or glass terrarium. Keep the terrarium covered securely while letting in air for them to breathe. Snails are strong and can easily push off a plastic lid, so secure the lid with rubber bands if necessary. Stock their habitat with several wet paper towels and vegetables from the grocery store (lettuce, carrots, apples, etc.). Twice a week, clean out their habitat by throwing away the old paper towels and food and giving them new wet paper towels and food. If you are keeping the snails longer than a week, place pieces of chalk in each container since they need calcium for shell growth and repair.

At the end of your project, snails may be released if they were collected locally. It is often interesting to “tag” the snails before you release them with a dot of nail polish on their shells. Thus, individuals may be tracked over time. If you choose not to release these pests back into your neighbors’ gardens, they may be frozen then thrown away. The adventurous can try cooking and eating them. That’s right! The garden snails found in North America are the same species that is used in escargot. In the going further section, there are resources for how to make escargot – although beware… this may be traumatic to some of your students.

Student Prerequisites
None required although familiarity with observation, measurement, and histograms is helpful (see Human Traits Survey lesson).

Getting Ready

  1. Prepare snail habitats and capture snails.
  2. Set shared materials in a central location for groups to access.

 

Snail Variations - Lesson Plan

Lesson Plan

  1. Discuss any ground rules (like do not hurt any snails) then jump right in! Pass out the snails, hand lenses, rulers, and stop watches. Ask groups to spend a few minutes observing the features and behavior of the snails.
  2. When students have had enough time to study the snails, have them close the lids. Ask students what they noticed. In particular, focus on how individual snails differ from one another. Discuss both the physical and behavioral traits of the snails.
  3. Ask students how these different physical and behavioral characteristics could be measured. Discuss the difference between subjective (bigger, faster, smarter) and objective (4.5 cm, travels 8 cm/min, figures out a maze in 2 min) measurements.
  4. Challenge students to pick a snail trait to measure. They should write down a procedure for their test and record the result for each snail that they were given. Everyone in the group must agree on the procedure such that the results would be the same, no matter who conducted the test. That means that your procedure should describe exactly what to do as if you were describing how to conduct the test over the phone to a friend. For instance, if you want to measure “size”, do you measure weight or length or width or height? If you measure length, what do you do when the snail is hiding inside its shell? Do you count antennae or not? Do you use centimeters or inches?
  5. Give students time to choose a trait, agree on a procedure and record their data. Circulate among the groups to help students that are struggling. Groups that finish early should be challenged to design a second procedure – possibly with the requirement that if they already tested a physical trait, that their second test should be of a behavioral trait.
  6. When all groups have finished, have them close the lids again. Discuss different ways to graphically present the results – pie charts, histograms, line graphs, etc. Tell students that they will be given 5 minutes to prepare a presentation for the rest of the class. Their presentation should include:
    • a description of their procedure
    • a table of results for their population of snails
    • a graphical presentation of their results

Snail Variations - Going Further

Assessment

  1. Students’ data and graphs can be collected and graded.
  2. Written protocols for trait measurements can be passed between groups so that students get practice and feedback on writing a scientific protocol. You may wish to do this before having each group graphically represent their data. This extension generates considerable discussion on the causes of experimental error and measurement inconsistencies. It also allows the full characterization of the population of snails on a wide range of traits.

Going Further

  1. Snails may be “tagged” with spots of nail polish then released into one or more environments (for instance, a school yard versus a vacant lot). Choose your environments carefully such that those areas actually can support a number of snails (a parking lot is probably not the best choice). Students can make hypotheses about which snails with what combination of traits will survive better in which environments. Changes in the populations’ traits may be monitored over time and may be correlated with the students initial hypotheses. In this way, students can ask very open ended questions about natural selection in the real world with living organisms. In the end, students may discover more about habitat choice and survival than natural selection per se, still it is an incredibly rich and varied exercise that the students thoroughly enjoy.
  2. As described previously, garden snails are escargot and are quite tasty if prepared properly. There are several steps to preparing your snails for the table:
    1. Feed your snails just cornmeal (3 tablespoons for a dozen snails) for approximately 4 days.
    2. Fast your snails in clean habitats with just wet towels for 2 more days.
    3. Just before cooking, rinse the snails in cool water from the tap.
    4. Plunge the snails into boiling water, shells and all. Boil uncovered for 2-3 minutes. A lot of foam will develop so watch carefully.
    5. Drain the snails and rinse with cold water. Using a toothpick, carefully pry each snail from its shell.
    6. The tightly coiled gall section of the snail that lies deepest in its shell should be cut off and discarded.
    7. The final cleaning step is to rinse the snails in water with a splash of vinegar until the water no longer turns cloudy.
    8. To cook the snails, boil 2 cups of snails in a broth made from 3 cups of beef broth, 1/2 cup white wine, 1 small chopped onion, 1 bay leaf, 1/2 teaspoon thyme, 1/2 teaspoon parsley, and salt and pepper to taste. Simmer for 1 hour.
    9. For the traditional preparation of escargot in garlic butter, melt 1 stick of butter (8 tablespoons) then add 1 1/2 teaspoons of chopped garlic, 1 tablespoon chopped green onion, and 2 tablespoons chopped fresh parsley. Puree the melted butter and seasonings in a food processor. Add salt and pepper to taste. Drizzle the garlic butter evenly over cooked escargot in an oven proof dish like a ramekin.
    10. Bake at 400 degrees for 7 –10 minutes.
  3. Investigate trait variations in plants. Grow plants in the classroom and compare trits such as plant height, color, time to flower opening, hairiness, and more. See the Raising Plants project for more details.

Snail Variations - Sources and Standards

Sources
This lesson was adapted from a lesson by Karen Kalamuck of the Exploratorium Teachers Institute.

For information on snails and snail care, see this website from the Lawrence Hall of Science.

The escargot recipe is taken from Gourmet Magazine, March 2001. A copy of this can be found at Epicurious.com.

Standards
Grade 7
Evolution
3. Biological evolution accounts for the diversity of species developed through gradual processes over many generations. As a basis for understanding this concept:
  a.    Students know both genetic variation and environmental factors are causes of evolution and diversity of organisms.

Investigation and Experimentation
7. Scientific progress is made by asking meaningful questions and conducting careful investigations. As a basis for understanding this concept and addressing the content in the other three strands, students should develop their own questions and perform investigations. Students will:
a.     Select and use appropriate tools and technology (including calculators, computers, balances, spring scales, microscopes, and binoculars) to perform tests, collect data, and display data.
e.     Communicate the steps and results from an investigation in written reports and oral presentations.

Grade 9-12
Evolution
7. The frequency of an allele in a gene pool of a population depends on many factors and may be stable or unstable over time. As a basis for understanding this concept:
a.     Students know why natural selection acts on the phenotype rather than the genotype of an organism.

8. Evolution is the result of genetic changes that occur in constantly changing environments. As a basis for understanding this concept:
a.     Students know how natural selection determines the differential survival of groups of organisms.
b.     Students know a great diversity of species increases the chance that at least some organisms survive major changes in the environment.

Investigation and Experimentation
1.  Scientific progress is made by asking meaningful questions and conducting careful investigations. As a basis for understanding this concept and addressing the content in the other four strands, students should develop their own questions and perform investigations. Students will:
a.     Select and use appropriate tools and technology (such as computer-linked probes, spreadsheets, and graphing calculators) to perform tests, collect data, analyze relationships, and display data.
b.     Identify and communicate sources of unavoidable experimental error.
c.     Identify possible reasons for inconsistent results, such as sources of error or uncontrolled conditions.

Sub Plan - DNA Jewelry

Summary
Students create DNA models from beads and wire that may be used as earrings, pendants, Christmas ornaments, and/or key chain pulls. This project is simple enough that a good substitute could lead the students through it since the content should be taught beforehand. More importantly, this is just one of many possible 3D DNA models you could have your students build. Be creative! Use gumdrops, Styrofoam, marshmallows, Legos, grapes, wood, aluminum cans, etc. Better yet, have your students design a model independently.

Objectives
Reinforce student understanding of the general structure of DNA and base pairing rules.

Vocabulary
DNA
Deoxyribose
Phosphate
Nucleic acid
Adenine
Thymine
Cytosine
Guanine
Base pairs
Nucleotide

AttachmentSize
Sub_DNA_Jewelry.doc71.5 KB
Sub_DNA_Jewelry.pdf65.68 KB

DNA Jewelry - Logistics

Time
45-50 minutes

Grouping
Individual

Materials
Each student needs:

  • 20 alphabet beads (6-7 mm) with the letters A, C, G, and/or T. Available for very reasonable prices ($2.00 for a bag of 100 beads) from Enterprise Art Item #1299011 (A), #1299013 (C), #1299013 (G), #1299030 (T)
  • 40 colored beads (6-7 mm) to represent phosphates. See Enterprise Art ($2.19 for a bag of 1000) Item #100420 (red).
  • 40 colored beans (6-7 mm) to represent sugars. See Enterprise Art ($2.19 for a bag of 1000) Item #100463 (turquoise).
  • 20-30 seed beads in assorted colors to represent hydrogen bonds. See Enterprise Art ($1.99 for 75 grams of assorted seed beads) Item #144117.
  • 40 cm of beading wire (26-28 gauge). See Enterprise Art ($2.54 per spool) Item #430602 (silver).
  • Optional: earring hooks, Christmas ornament wires, wire loops for pendants, key rings, etc. See Enterprise Art ($2.54 for 48 fishhook earring hooks) Item #144202 (silver).

Groups of 4-6 students need:

  • Small condiment cups and trays on which to organize and set out materials.
  • Wire cutters. (Do not use scissors! They will be ruined.)

Setting
Classroom

Teacher Background
See Teacher Background in Paper DNA Models Lesson.

Student Prerequisites
Good understanding of DNA structure. See Paper DNA Models Lesson.

DNA Jewelry - Getting Ready

Getting Ready

  • Order beads (they take approximately 2 weeks to arrive from Enterprise Art)
  • Organize beads so that each tray contains enough materials for each group of 4-6 students. You may want to precut the wire as well to avoid the delay of passing the spools of wire around the room.
  • Optional: write the step by step guide onto the board or photo copy the instructions for each group of students.

DNA Jewelry - Instructions

Instructions

  1. String the following onto your wire: phosphate – sugar – base – correct number of seed beads (2 for A-T, 3 for C-G) – matching base – sugar – phosphate.
  2. Onto one end, add: a base – correct number of seed beads (2 for A-T, 3 for C-G) – matching base. Do not push these beads down to meet the others.
  3. Feed the free end through the beads you just added.
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  4. Pull the wire ends tight to form a loop. Then add to both free ends: sugar – phosphate. These may be pushed down to meet the others.
  5. Repeat steps 2-4 until you have added as many rungs to your DNA ladder as you want.
  6. To make the very last rung on your DNA and to tie it off, add one base to a free end and add its matching base to the other free end. These may be pushed down to meet the others.
  7. Onto one end, add the correct number of seed beads (2 for A-T, 3 for C-G). Do not push these beads down to meet the others.
  8. Feed the free end through the beads you just added.
  9. Pull the wire ends tight to form a loop. If you wish to add an earring hook, loop, key ring, Christmas ornament wire, or other doo dad, add it to one free end.
  10. Twist the wire ends together tightly. Cut the wire off 3-4 mm from the base of the twist.
  11. Finally, add a slight counter-clockwise twist to the entire DNA molecule to form a double helix. You have now made lovely DNA jewelry!

DNA Jewelry - Sources and Standards

Sources
This activity was adapted from a DNA earring design by Karen Kalamuck of the Exploratorium Teacher Institute and from the “Modeling DNA, the Code of Life” activity by the RAFT Education Department. I recently discovered another write up for this activity by Catherine Ross .

Standards
Grade 7
Genetics
2. A typical cell of any organism contains genetic instructions that specify its traits. Those traits may be modified by environmental influences. As a basis for understanding this concept:
e.    Students know DNA (deoxyribonucleic acid) is the genetic material of living organisms and is located in the chromosomes of each cell.

Grades 9-12
Genetics
5. The genetic composition of cells can be altered by incorporation of exogenous DNA into the cells. As a basis for understanding this concept:
a. Students know the general structures and functions of DNA, RNA, and protein.
Students know how to apply base-pairing rules to explain precise copying of DNA during semiconservative replication and transcription of information from DNA into mRNA.