Cystic fibrosis and sickle cell anemia are examples of what?

• A. Sex determination
• B. Test cross
• C. Incomplete dominance
• D. Common genetic disorders

Answer: (D)

These show how a genetic change in a single gene can cause disease and be passed down through generations. Cystic fibrosis is caused by mutations in the CFTR gene, and sickle cell anemia by a mutation in the beta-globin gene. Both are inherited disorders, typically transmitted in autosomal recessive fashion, meaning an individual usually must inherit two faulty copies to express the full disease, while carriers with one copy are often healthy but can pass the allele on. This makes them classic examples of genetic disorders. They aren’t about determining sex, they aren’t about a breeding test, and they don’t illustrate incomplete dominance in the usual sense, since the disease phenotype isn’t an intermediate form in heterozygotes.