In cattle, roan coat color (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?

(A) Red * red.

(B) Red * roan.

(C) Roan * roan.

(D) Red * white.

(E) White * roan.

C

Explanation:

They tell us that the roan coat color occurs in heterozugous offspring from homozygous red and white parents, therefore we can assume that the answer will not be A because they are both red.

In B there would be a cross between

CRCR x CRCW

this would yield 2 roan offspring and 2 red offspring, but no white offspring, therefore we know this is not our answer.

In D we know that red and white homozygote parents only produce roan offspring, but no red or white offspring, therefore we know this is not our answer.

In E there would be a cross between

CWCW x CRCW

this would yield 2 roan offspring and 2 white offspring, but no red offspring, therefore we know this is not our answer.

In C there would be a cross between

CRCW x CRCW

this would yield 1 red individual, 2 roan individuals and 1 white individual, which is the answer we are looking for.

Therefore the answer is C.

Option C

Explanation:

Given -

Genotype of mixed red and white haired (roan colored) cattle - CRCW

Genotype of red colored cattle - CRCR

Genotype of white colored cattle - CWCW

Now when a roan cattle is mated with another roan cattle the following offsprin are produces

CRCW * CRCW

CRCR, CRCW, CRCW, CWCW

Thus -

CRCR - red cattle - 1

CRCW - Roan cattle - 2

CWCW - white cattle - 1

Hence, option C is correct