Question

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 $x$?

• A. 3
• B. 9
• C. 15
• D. 25

Answer 1

Answer: (C)

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 $1 + 6 + 2 x + 20 + 6 + 1 = 64$
$2x=64-34$
$x=\frac{30}{2}=15$