Question

Case: Purebred shorthorn cattle of white coat (WW) were crossed with purebred cattle of red coat (RR). The $F_1$ cattle had coats with patches of white and red side by side.

But in certain condition, if a shorthorn cattle of white coat (WW) was crossed with a cattle of red coat (RR) resulted in all pink coated cattles. Then, what are the chances of the appearance of red coat in a cross between pink coated and white coated cattles?

• A. 25%
• B. 50%
• C. 75%
• D. 0%

Answer 1

The correct option is D 0%

If the red and white coated cattles produce pink colour on a cross then, they exhibit incomplete dominance in the inheritance of coat colour due to which they produce pink coloured coat upon hybridisation.

If pure breeding red coated cattles are represented as ‘RR’ and pure breeding white coated as ‘WW’, then the pink coated cattles are ‘RW’.

A cross between ‘RW’ and ‘WW’ would produce pink coated cattles (RW) and white coated catlles (WW) in the ratio of 1 : 1

Hence, there are zero chances of getting a red coated cattle (RR).

Parents: RW (Pink) X WW (White)
Gametes: R W W

$\begin{array}{ccc}& \text{R}& \text{W}\\ \text{W}& \text{RW (Pink)}& \text{WW (White)}\end{array}$