What is epistasis?

Epistasis refers to a genetic interaction where the expression of one gene is affected by one or multiple other genes. More specifically, in cases of epistasis, one gene can mask or modify the effect of another gene on the phenotype. This means that the presence of a specific allele at one locus may completely suppress or alter the expression of alleles at another locus, leading to variations in traits that wouldn't occur if those genes operated independently.

For instance, in certain coat color patterns in animals or in the expression of specific diseases, the interaction between different genes can lead to unexpected phenotypic outcomes, illustrating the complexity of gene regulation and expression. Understanding epistasis is essential in genetics because it highlights how traits can be influenced by the interaction of multiple genes rather than by single gene inheritance alone.

The other choices, while related to genetics, describe different concepts. For example, genes that influence the same trait can occur independently without one masking the other, multiple gene interactions can occur without one allele's expression being completely obscured, and dominance relationships examine how alleles interact at a single locus rather than how they influence each other across different loci.