Which genetic disorder is a result of a mutation that can be traced through families?

Hemophilia is indeed a genetic disorder that results from mutations in genes responsible for the production of blood clotting factors. One of the most common forms is hemophilia A, which is linked to a mutation in the factor VIII gene. The condition is inherited in an X-linked recessive manner, meaning it is commonly passed from carrier mothers to affected sons. This type of inheritance pattern allows hemophilia to be traced through families, with affected individuals often found in successive generations, revealing its familial nature.

The other disorders listed have different inheritance mechanisms or causes. Down syndrome, for instance, is primarily caused by chromosomal abnormalities (specifically trisomy 21) and is not directly inherited in a familial pattern. Cystic fibrosis is caused by mutations in the CFTR gene and can also be hereditary, but its inheritance is autosomal recessive rather than specifically tied to a lineage like hemophilia. Fragile X syndrome is associated with a mutation in the FMR1 gene and follows an X-linked inheritance pattern as well, but is characterized by a repeat expansion that does not typically show the same direct lineage tracing seen with hemophilia, especially since the penetrance can vary widely among females. Thus, hemophilia stands out as the