Which statement best describes the inheritance of cystic fibrosis in terms of the CFTR gene?

• A. It is autosomal recessive; carriers are usually unaffected, and an individual must inherit two mutated copies to be affected.
• B. It is X-linked.
• C. It affects males only.
• D. It is autosomal dominant.

Answer: (A)

Cystic fibrosis is inherited in an autosomal recessive pattern: the CFTR gene is on an autosome, so both sexes are affected equally. A person must inherit two mutated copies of CFTR to develop the disease, while someone with just one mutated copy is a carrier who usually doesn’t show symptoms because one normal copy provides enough CFTR protein. This means two carrier parents have a 25% chance to have an affected child, a 50% chance to have a carrier child, and a 25% chance to have a child with two normal copies.