Polygenic inheritance, also known as quantitative inheritance, is the gene interaction in which a given trait is conditioned by several different genes having alleles that may or may not contribute to increase the phenotype intensity. The alleles may be contributing or noncontributing and there is no dominance among them. Polygenic inheritance is the type of inheritance, for example, of skin color and of stature in humans.

Considering a given species of animal in which the length of the individual is conditioned by polygenic inheritance of three genes, for the genotype having only noncontributing alleles (aabbcc) a basal phenotype, for example, 30 cm, would emerge. Considering also that for each contributing allele a 5 cm increase in the length of the animal is added, so in the genotype having only contributing alleles (AABBCC) the animal would present the basal phenotype (30 cm) plus 30 cm more added by each contributing allele, i.e., its length would be 60 cm. In the case of triple heterozygosity, for example, the length of the animal would be 45 cm. That is the way polygenic inheritance works.   _{Your Comment}