Question

Describe quantitative inheritance controlled by two pairs of genes. 

Answer 1

1. Quantitative inheritance is also known as polygenic inheritance in which characters are determined by two or more gene pairs which have additive or cumulative effect. These genes are called cumulative gene or polygenes.
2.  This quantitative inheritance can be explained by wheat kernel colour which is controlled by two pairs of genes Aa and Bb.
3.  H. Nilsson Ehle crossed red kernelled variety of wheat with white kernelled variety.
4. Gene A and B determine the red colour of kernel (responsible for producing red pigment) and are dominant over their recessive allele a and b which do not produce red colour pigment and the expression is white, if dominant gene is not present. Thus, genotype of a parent with
   red kernels is AABB and that of parent with white kernels is aabb. Genotype of F1 hybrids is AaBb.
5.  Continuous variations in expressions is observed as each dominant gene produces specific amount of pigment and the shade of red colour, depends on number of dominant gene present
   as shown in Punnett square.
6. 
7.