Epistasis

Definition
noun, plural: epistases
(genetics) The interaction between nonallelic genes at two or more loci resulting in one gene masking the phenotypic expression of another gene
(medicine) The arrest of a secretion or bodily discharge
Supplement
In genetics, epistasis pertains to the interaction of the genes at two or more loci, and as a result the effect of the gene depends on the presence of one or more modifier genes. There is that one gene or allele masking the phenotypic expression of the other genes or alleles in the interaction. That gene or allele masking the effect is referred to as epistatic. In contrast, the other gene(s) or allele(s) being masked is/are referred to as hypostatic. Epistasis may be recessive or dominant. An example of epistasis is the fur color of Labrador retrievers, which is a polygenic trait. Two genes are interacting to determine its fur color. One gene (represented by B) determines the fur color whereas the other gene (represented by E) controls the expression of the gene B. The presence of homozygous recessive alleles ee would mask the gene B (regardless of the dominant B alleles). This is an example of recessive type of epistasis.
Word origin: Greek epístasis (stopping, stoppage)
See also:

• locus
• gene