Question

In cattle, roan coat color (mixed red and white hairs) occurs in the heterozygous (Rr) offspring of red (RR) and white (rr) homozygotes. Which of the following crosses would produce offspring in the ratio of 1 red:2 roan:1 white?
A) red × white
B) roan × roan
C) white × roan
D) red × roan
E) The answer cannot be determined from the information provided.

Answer 1

The answer is B) roan x roan.

Let's summarize:
R - dominant allele,
r - recessive allele,
RR - dominant homozygous with red color,
rr - recessive homozygous with white color,
Rr - heterozygous with roan color.

If we cross two heterozygous (Rr):

Parents:         Rr     x     Rr
Offspring:      RR   Rr   Rr   rr

then, the offspring will be: 1 red (RR) : 2 roan (Rr, Rr ) : 1 white (rr).