What is the genetic interaction where one gene masks or modifies the effect of another called?

The correct term for the genetic interaction where one gene masks or modifies the effect of another is epistasis. This phenomenon occurs when the expression of one gene interferes with or completely suppresses the expression of another gene, regardless of the alleles present at the second gene locus.

For example, in certain coat color patterns in mice, one gene may control whether pigment is produced, while a second gene determines the type of pigment. If the first gene is not activated (in a homozygous recessive state), it can mask the effects of the second gene, regardless of its alleles. Epistasis highlights the complexity of genetic interactions beyond simple dominance and recessiveness, illustrating how multiple genes can influence a single phenotype.

Understanding epistasis is essential for interpreting genetic crosses and predicting phenotypic ratios, especially in more complex traits influenced by multiple genes.