Genes that are located in different parts of the chromosomes and are responsible for coding various proteins. Unlike allelic genes, they are not paired variants of the same gene, but are completely different genetic units. There are several forms of interaction of non-allelic genes:
1) complementarity (addition of one gene by another),
2) epistasis (suppression of the action of one gene by another),
3) polymerization (the summative effect of several genes on one trait), and
4) pleiotropy (the action of one gene on several traits).