Question

For a quantitative trait observed in the F2 generation, the number of individuals showing one of the extreme phenotypes was 51 out of a total of 798 F2 progeny. Therefore the number of genes pairs involved in controlling the trait being studied, under the given set of experimental conditions is:

A. 1 B. 2 C. 3 D. 4 E. 16

Please show working.

Answer 1

Choice B is correct

Reason: In polygenic inheritance, it can be deciphered that the extreme phenotypes are the terminal phenotypes which arise due to presence of total genes in the offsprings. The mathematical equation which can be directly used to calculate the number of genes involved in the phenotype can be given by:

1/4ⁿ, where n is the number of genes observed and thus, 4ⁿ refers to number of genes involved.

Here, the fraction of extreme phenotype is 51/798 or nearly 1/16

Thus, according to this equation, we can have here, 1/16 or 1/4²

This gives value of n=2.

Thus, only two genes are involved in this mode of inheritance.