What is "epistasis"

"the checking of a discharge," medical Latin, from Greek epistasis "a stopping, stoppage, a halting," from epi "upon" (see epi-) + stasis "a stopping or standing" (see stasis).

n. (context genetics English) The modification of the expression of a gene by another unrelated one

n. the suppression of a gene by the effect of an unrelated gene [syn: hypostasis]

Epistasis is the phenomenon of the effect of one gene being dependent on the presence of one or more 'modifier genes', the genetic background. Thus, epistatic mutations have different effects in combination than individually. It was originally a concept from genetics but is now used in biochemistry, computational biology and evolutionary biology. It arises due to interactions, either between genes, or within them, leading to non-additive effects. Epistasis has a large influence on the shape of evolutionary landscapes, which leads to profound consequences for evolution and evolvability of phenotype traits.