What is polygenic inheritance? How does it work?

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

Considering a given species of the 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 instance, 30 cm, would emerge. Considering also that for every 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 that is its length would be 60 cm. In case of triple heterozygosity, for instance, the length of the animal would be 45 cm. i.e. the way the polygenic inheritance works.