Question

A roan bull is bred to three cows. Cow A has the same genotype as the roan bull. Cow B is red and cow C is white. What proportions of roan cows are expected in the offsprings of each group of cows?

• A. 2, 1, 1
• B. 1, 2, 1
• C. 1, 1, 2
• D. 3, 1

Answer 1

The correct option is A 2, 1, 1

Coat colour in cows is governed by two alleles; W (red) and w (white). These two alleles show codominance and the hybrid genotype (Ww) has a roan coloured coat. The genotype of a roan cattle is "Ww", that of red is "WW" and that of a white one is "ww". A cross between a roan bull and roan cow produces red, roan and white phenotypes in 1:2:1 ratio respectively. A cross between roan bull (Ww) and red cow (WW) produces roan and red phenotypes in 1:1 ratio. A cross between roan bull (Ww) and white cow (ww) produces roan and white phenotypes in 1:1 ratio. The proportions of roan cows in the offspring of each group of cow is 2,1,1. Thus, the correct answer is option A.