What genetic phenomenon involves an interaction between genes where one gene masks the expression of another?

The phenomenon being described is epistasis, which occurs when the expression of one gene is completely masked or altered by the presence of another gene. This type of interaction can significantly influence the phenotype of an organism, as the effects of one gene can depend on the presence or absence of another gene. For example, in certain genetic pathways, a mutation in one gene can prevent the product of another gene from being expressed at all, thereby altering the expected traits that would typically arise based on Mendelian inheritance.

Epistasis is important in understanding complex traits and diseases, as it highlights that the relationship between genes is not always additive. Different combinations of alleles can lead to various phenotypes due to these interactions, showcasing the complexity of genetic inheritance beyond simple dominant and recessive patterns.

In contrast, the other options refer to different concepts. Polygenic inheritance involves multiple genes contributing to a single trait, rather than one gene affecting the expression of another. Genetic drift refers to random changes in allele frequencies that occur in a population, often due to chance events, and is related to population genetics rather than direct gene interactions. Allelic variation pertains to the different forms of a gene (alleles), which may contribute to diversity within a trait but does not specifically indicate a