Cystic fibrosis is caused by mutations on which chromosome?

• A. Chromosome 7
• B. Chromosome 3
• C. Chromosome 11
• D. Chromosome 13

Answer: (A)

Cystic fibrosis arises from mutations in the CFTR gene, which provides the instructions for making the CFTR chloride channel on epithelial cell surfaces. This gene is located on chromosome 7, specifically in the region 7q31.2. When CFTR is mutated, chloride and water transport across surfaces like the airways and pancreas is disrupted, leading to the thick, sticky mucus characteristic of the disease. The most common mutation, ΔF508, causes the protein to misfold and be degraded before it reaches the cell membrane, reducing functional channels.

Because CF is inherited in an autosomal recessive manner, two defective copies are needed for disease to manifest; individuals with one mutated copy are typically carriers without symptoms. The other chromosomes mentioned do not carry the CFTR gene, so mutations there are not what causes cystic fibrosis.