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. red × roan
d. white × roan
Answer: b. roan × roan