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

Question

A polygenic trait is controlled by 3 genes A, B and C. In a cross AaBbCc × AaBbCc, the phenotypic ratio of the off springs was observed as 1: 6: ×: 20: ×: 6: 1 What is the possible value of x? (A) 3 (B) 9 (C) 15 (D) 25

Tardigrade Admin · Accepted Answer

Polygenes show polygenic inheritance or quantitative inheritance. As genes are present on different chromosomes they will segregate independently during meiosis. Number of individuals in

F_{2} = 4^{n}

n

=number of genes present

= 4^{3} = 64

individuals

1 + 6 + 2 x + 20 + 6 + 1 = 64

2 x = 64 - 34

x = \frac{30}{2} = 15

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

3

9

15

25

Polygenes show polygenic inheritance or quantitative inheritance. As genes are present on different chromosomes they will segregate independently during meiosis. Number of individuals in F2​=4n n =number of genes present =43=64 individuals 1+6+2x+20+6+1=64 2x=64−34 x=230​=15

Q. A polygenic trait is controlled by 3 genes A, B and C. In a cross AaBbCc $\times$ AaBbCc, the phenotypic ratio of the off springs was observed as $1 : 6 : \times : 20 : \times : 6 : 1$ What is the possible value of $x$ ?