A gene that by itself has little effect on the phenotype but which can act together with others to produce observable variations WordNet 3.0 & Open English WordNet

A polygene is a member of a group of non-epistatic genes that interact additively to influence a phenotypic trait, thus contributing to multiple-gene inheritance, a type of non-Mendelian inheritance, as opposed to single-gene inheritance, which is the core notion of Mendelian inheritance. Wikipedia

Member of a group of genes that interact additively to influence a phenotypic trait Wikidata

Trait controlled by several genes, as opposed to monogenic. OmegaWiki

A group of nonallelic genes that act together to produce phenotype variations. Wiktionary