Zoology - Principles of Inheritance and Variation Question with Solution | TestHub

The traits generally controlled by three or more genes are called as polygenic traits. Human skin colour is a classic example of this. In a polygenic trait, the phenotype reflects the contribution of each allele, i.e, the effect of each allele is additive. To understand this better, let us assume that three genes A, B, C control skin colour in human, with the dominant forms A, B and C responsible for dark skin colour and the recessive forms a, b and c for light skin colour. The genotype with all the dominant alleles (AABBCC) will have the darkest skin colour and that with all the recessive alleles (aabbcc) will have the lightest skin colour. As expected, the genotype with three dominant alleles and three recessive alleles will have an intermediate skin colour.