Which scenario is an example of epistasis?

The scenario depicting a missing enzyme blocking a metabolic pathway serves as a clear example of epistasis because it illustrates how one gene can influence or mask the expression of another gene. In this context, the missing enzyme acts as an epistatic gene, preventing the metabolic pathway from functioning properly, which in turn affects the phenotype. This interaction highlights the hierarchical nature of gene expression, where one gene’s product can determine whether another gene will be expressed or contribute to a particular trait.

In contrast, the other scenarios do not exemplify epistasis as effectively. While two alleles affecting flower color could indicate interaction or dominance relationships among alleles, it does not inherently show one gene masking another. The inclusion of multiple alleles for blood type represents a case of multiple allelism rather than epistasis, where each allele contributes to the phenotype without one being dominant over the others. Lastly, a trait affected by several independent genes reflects polygenic inheritance, where multiple genes contribute to a single trait, but it does not illustrate the concept of one gene overshadowing or suppressing another.