Question

In a polygenic cross aabacc × aabbcc the phenotypic ratio offspring is 1: 6'x' : 20x : 6 : 1 what is the value of' x'

Answer 1

0Q:

A polygenic trait is controlled by 3 genes A, B and C. In a cross AaBbCc x AaBbCc, the phenotypic ratio of the offsprings was observed as 1 : 6 : m : 20 : m : 6 : 1. What is the value of m?

A) 10

B) 15

C) 18

D) 24

Answer: B) 15

Explanation:

Here crossing is AaBbCc x AaBbCc

As it is trihybrid cross,

we know, Number of zygotes formed = 4n, where n = 3

43 = 64

Given ratio of offsprings = 1 : 6 : m : 20 : m : 6 : 1

Now, 1 + 6 + m + 20 + m + 6 + 1 = 64

34 + 2m = 64

2m = 30

=> m = 15.