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.