Question

In mice, agouti fur is a dominant trait resulting in individual hairs having a light band of pigment on an otherwise dark hair shaft. A mouse with agouti fur is shown here, along with a mouse with solid color fur, which is the recessive phenotype (A = agouti; a = solid color).A separate gene, which is not linked to the agouti gene, can result in either a dominant black pigment or a recessive brown pigment (B = black; b = brown).A litter of mice from the mating of two agouti black parents includes offspring with the following fur colors:* solid color, black * solid color, brown (sometimes called chocolate) * agouti black * agouti brown (sometimes called cinnamon) What would be the expected frequency of agouti brown offspring in the litter?

Answer 1

Below are the choices that can found elsewhere. 

A) 3/16
B) 1/8
C) 9/16
D) 1/2
E) 1/4
F) not enough information given

The answer is A because the two traits are determined by unlinked genes, they assort independently. As a result, you need to use the multiplication rule to calculate the probability of agouti brown offspring (A_ bb) from AaBb parents. The probability of A_offspring is 3/4, and the probability of bb offspring is 1/4. The combined probability is therefore 3/4 x 1/4 = 3/16.