Polygenic (or Quantitative) inheritance is that type of inheritance in which the complete expression of a trait is controlled by two or more genes in which a dominant allele of each gene contributes only a unit fraction of the trait and total phenotypic expression is the sum total of a additive or cumulative effect of all the dominant alleles of genes\/polygenes. Human skin colour is an example of such polygenic inheritance which is controlled by three pairs of polygenes A,B and C. Negro\/black colour is due to presence of all the six dominant contributing alleles AABBCC. Very light colour or white colour is due to presence of all six recessive non-contributing alleles aabbcc.