Question

The grain colour of wheat is determined by the additive effects of two pairs of genes. Accordingly, the F2 inheritance appears in the ratio of 15 red, 1 white. The fifteen red appears in different shades in the ratio of
A. 9:3:3
B. 6:6:3
C. 1:4:7:3
D. 1:4:6:4

Answer 1

Hint: When a single character is being controlled by either two or more genes together, the phenomenon is known as polygenic inheritance. Polygenes exist in a wide variety of organisms. The grain colour in wheat is associated with the phenomenon of polygenic inheritance.

Complete answer: The above case occurs with polygenic inheritance. In the case of grain colour in wheat, the colour of the kernel is controlled by two different genes, in which each of it has two alleles each. The red kernel colour is dominant over the white colour. When the two purebred varieties of red and white kernel bearing plants were crossed and the F1 progeny thus, produced were again crossed with each other to produce the F2 generation: four different kinds of red colours were present in the plants possessing the dominant ‘R’ allele and the ones which were devoid of ‘R’ were white in colour. The ratio of different shades thus produced were 1:4:6:4 of red colours ranging from dark red to medium red colours and only 1 white coloured kernel was produced. Thus, a bell-shaped curve was formed.
The other given ratios don’t correspond to the theory of polygenic inheritance, thus the most appropriate and correct option was 1:4:6:4.
Thus, option D is the correct answer.

Note: The theory of polygenic inheritance was first discovered by Nilsson and Ehle in 1909. The phenomena were found to be compatible with the Mendelian Laws and explain the Inheritance of continuous traits. Here, a single trait is influenced by a group of genes in combination. Later studies proved that these genes were not linked and underwent independent assortment.