What is the definition of gene interaction?

Gene interaction is the process by which two or more pairs of genes, with independent distribution, jointly condition a single trait. Gene interaction occurs when the interaction between the products of gene pairs generates new effects or qualities different from those resulting from the expression of only one of these pairs in isolation. Epistasis is a type of gene interaction in which genes of one pair of alleles inhibit the manifestation of genes of other pairs. In pleiotropy, a single pair of genes acts on the manifestation of several traits.