Swedish geneticist H.Nilsson-Ehle (1908) discovered the polygenic inheritance. He crossed red kernelled variety of wheat with white kernelled variety. In F1 generation all plants had grains with intermediate colour between red and white and in F2 generation five different phenotypic expressions appeared in the ratio 1:4:6:4:1. (Instead of red, intermediate and white in the ratio, 1:2:1). Continuous variations in the expression were as follows,
1. The darkest red (as red as the parent plant) - 1/16
2. Medium red (less than parent plant but more than F1 hybrids) - 4/16
3. Intermediate red (as F1 hybrids) - 6/16
4. Light red (less than F1 hybrids) - 4/16
5. White (as white as parent plant) -1/16
Nilsson Ehle suggested that the Kernel colour in wheat is controlled by two pairs of genes, Aa and Bb.
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 kernels is aabb. Genotype of F1 hybrids is AaBb. During gamete formation each gene pair shows Mendelian segregation and four types of gametes are produced. Continuous variations (gradations) in expressions is observed as each dominant gene produces specific amount of pigment and she shade of red colour, (dark and light) depends on number of dominant genes present as shown in the following Punnett square. Only one, out of sixteen is with four dominant genes and is the darkest red. Four, out of sixteen have three dominant genes and are medium red, six have two dominant genes and are intermediate red, four have only one dominant gene and are light red and again only one is with out any dominant gene and is therefore with white kernel colour.