Epistasis

n. exclusion of a gene by the effect of another unrelated gene (Genetics); stoppage of a secretion (Medicine)

Epistasis is the interaction between genes. Epistasis takes place when the action of one gene is modified by one or several other genes, which are sometimes called modifier genes. The gene whose phenotype is expressed is said to be epistatic, while the phenotype altered or suppressed is said to be hypostatic.
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E·pis·ta·sis n. pl. e·pis·ta·ses 1. A film that forms over the surface of a urine specimen. 2. An interaction between nonallelic genes, especially [more]Epistasis - Community and Resources

Noun
1. the suppression of a gene by the effect of an unrelated gene
(synonym) hypostasis
(hypernym) organic process, biological process

The influence of a gene on the expression of another (non-allelic) gene.