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.
Reinforce and assess students understanding of real world genetics issues.
Cystic 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.
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.
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.
Sickle Cell Anemia
Sickle 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.
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
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”.
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.
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!