What is the genotype of the female guinea pig?
Assume that brown eyes (B) are dominant over tan eyes (b) in guinea pigs. When a brown-eyed male is mated with a tan-eyed female, 50% of the litter has brown eyes and 50% has tan eyes.
It might appear that you need to do a test cross to solve this problem, but the problem tells us the femaile guinea pig has tan eyes which is the recessive trait. The only way for her to express the recessive trait is to be homozygous recessive for eye color. Therefore, letter D would the correct choice.