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?
none

1/8

3/16

1/4

1/2

9/16

not enough information given

The correct answer is explained below:

Explanation:

Fur characteristics in mice can be determined by two separate genes which are not linked to each other.One gene determines the bands of pigmentation in fur.The Agouti fur is dominant over the solid fur.Let Agouti be represented by A allele and solid fur be represented by a allele.The other gene determines the pigment in the color of the fur. The black pigment is dominant over the brown pigment.Let black color be represented by B allele and brown color be represented by b allele.In the given question two agouti black parents are crossed.The genotypes of the parents can be AABB or AaBb, that is, the parents can be either homozygous or heterozygous for both the genes.Among the offspring as four different phenoypes are found so we can conclude that both the parents are heterozygous for both the genes, that is,their genotypes are AaBb.This is because crossing parents who are homozygous for both the genes, that is, AABB would produce offfspring of only a single genotype, that is, AaBb and phenotype, agouti and black.The gametes produced by each of the AaBb parents: AB, Ab, aB, ab.Crossing the parents with AaBb genotype and agouti black phenotype we get,

             AB                        Ab                        aB                         ab

AB       AABB                 AABb                    AaBB                   AaBb

 (Agouti/Black)   (Agouti/Black)     (Agouti/Black)   (Agouti/Black)

Ab       AABb                  AAbb                    AaBb                   Aabb

  (Agouti/Black) (Agouti/Brown) (Agouti/Black)  (Agouti/Brown)

aB       AaBB                   AaBb                    aaBB                    aaBb

  (Agouti/Black)     (Agouti/Black)     (Solid/Black)     (Solid/Black)

ab       AaBb                   Aabb                     aaBb                    aabb

 (Agouti/Black)   (Agouti/Brown)   (Solid/Black)     (Solid/Brown)

The above dihybrid cross shows the possible genotypes and phenotypes of the offspring.Here, the frequency of Agouti/ Black offspring is: .The frequency of Agouti/ Brown offspring is: .The frequency of Solid/ Black offspring is: .The frequency of Solid/ Brown offspring is: .Hence, the answer to the question about the frequency of agouti brown offspring is: .