In cattle, roan coat colour (mixed red and white hairs) occurs in the heterozygous (CRCW) offspring of red (CRCR) and white (CWCW) homozygotes. Which of the following crosses would produce offspring in the ratio of 1 red:2 roan:1 white?

Question

Quizplus · Accepted Answer

The roan coat color is the result of heterozygosity. A roan cow (CRCW) can produce three types of gametes: CR and CW, each with a 50% probability. When two roan cows are crossed, each can produce the following gametes: CR or CW, each with a 50% probability. Therefore, the possible genotypes and phenotypes in the offspring are:

- 25% CRCR (red)
- 50% CRCW (roan)
- 25% CWCW (white)

This is the required ratio, and it can only be obtained by crossing two roan cows (B). Option A would produce entirely roan offspring. Option C would produce 50% white and 50% roan offspring. Option D would produce different ratios of each phenotype.

In Cattle, Roan Coat Colour (Mixed Red and White Hairs)