Cystic fibrosis is the most common metabolic error in European-derived (“white”) populations, with about 1 of every 1,600 being a carrier. Individuals born with cystic fibrosis are lacking an enzyme that allows them to break down thick mucus in the lungs and makes them susceptible to serious and often fatal lung infections. With aggressive treatment, most individuals may reach adulthood; otherwise death from pneumonia is likely in childhood. There is no cure; however, genetic engineering offers promise for these affected individuals. Cystic fibrosis is inherited as a recessive, and individuals with one copy of the gene are carriers of the disease. The gene has been located in chromosome 7.

 

Note: “normal” means that the individual does not phenotypically show the trait (hint- we don’t know the genotype of this person! There are two potential genotypes that could produce a “normal” phenotype). A “carrier” is someone who is phenotypically normal but who carries a gene for the trait (hint: we do know the genotype for a person like this… what is it?). Being “affected” with cystic fibrosis means that the individual has the disease, and is not just a carrier (hint- we do know the genotype for a person like this… what is it?).

 

A. What percentage of the gametes of a heterozygote individual will contain the recessive allele?
B. Draw a Punnett square (On your own, this is not graded).	xxxxxxxxxxxxxxxxxxxx
C. What percentage of the offspring will be affected with cystic fibrosis? (see above for definition of “affected”)
D. What percentage of the offspring will be normal? (see above for definition of “normal”)
E. What percentage of the offspring will carry the trait? (see above for the definition of a “carrier”)
F. Is it possible for an affected child to be born to non-carrier and carrier parents?  Why?