Polygenic inheritance is one of the exceptions to Mendel's law. One trait is influenced by more than one independent allele. Each allele has a cumulative or additive effect. Multiple genes produce an additive effect. Polygenic variation is characterised by the continuous variation of the phenotype of the trait. There are various examples of polymeric inheritance such as human height, and skin color of humans. There are almost 400 genes responsible for height. And the environment greatly influences the expression of these genes.