polygene

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun Any of a group of nonallelic genes, each having a small quantitative effect, that together produce a wide range of phenotypic variation.

from The Century Dictionary.

• Noting those volcanic cones which are the result of successive eruptions: contrasted with monogene. The term was suggested by A. Stübel.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun genetics A group of nonallelic genes that act together to produce phenotype variations

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun a gene that by itself has little effect on the phenotype but which can act together with others to produce observable variations