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 on chromosome 7.

a. What percentage of the gametes of a heterozygote individual will contain the recessive allele?

b. Draw a Punnett square crossing two individuals who are heterozygous for this trait.

c. What percentage of the offspring will be affected with cystic fibrosis?

d. What percentage of the offspring will be normal?

e. What percentage of the offspring will also carry the trait?

f. Is it possible for an affected child to be born to one healthy parent and one carrier?