What genetic mechanism explains the absence of albinism in children of two affected parents?

• A. Germinal mosaicism
• B. Variable expressivity
• C. Genetic heterogeneity
• D. Pleiotropy

Answer: (C)

The absence of albinism in children of two affected parents can be attributed to the concept of genetic heterogeneity. Genetic heterogeneity refers to the phenomenon where a single phenotypic trait or disorder can be caused by different genetic variations or mutations. In the case of albinism, there are several genes involved that can lead to the condition, and each parent may have different mutations that do not necessarily combine to produce the trait in their offspring.

For instance, if both parents are carriers of distinct mutations in genes responsible for melanin production, such as the TYR or OCA2 genes, their children might inherit one non-mutated allele from each parent. This combination would result in children who do not express the phenotype of albinism, despite both parents being affected individuals. The key here is the presence of different genetic causes that can lead to the same phenotypic outcome, which allows for situations where affected parents can have non-affected children due to the specific combinations of alleles inherited.