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 raction 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 noncontributing alleles aabbcc.