Hemophilia is an example of which genetic phenomenon?

• A. Allelic heterogeneity
• B. Phenotypic variation
• C. Locus heterogeneity
• D. Dominant-negative mutation

Answer: (C)

Hemophilia is primarily characterized as an example of locus heterogeneity. Locus heterogeneity occurs when mutations at different genetic loci can produce the same phenotype or disease. In the case of hemophilia, specifically hemophilia A is usually caused by mutations in the factor VIII gene located on the X chromosome, while hemophilia B is caused by mutations in the factor IX gene, which is also on the X chromosome. Both types lead to similar bleeding disorders despite being caused by mutations in different genes.

This distinction is important because understanding that multiple genes can contribute to the same phenotype highlights the complexity of genetic diseases and the necessity of considering various genetic factors when diagnosing and studying such conditions.

Other options refer to different genetic concepts, like allelic heterogeneity, which involves different mutations within the same gene leading to similar conditions, or dominant-negative mutations, which describe a mutation that not only leads to loss of function but also interferes with the normal allele's function. These concepts do not encompass the essence of hemophilia as well as locus heterogeneity does.