In rats, gene B produces black coat color if the genotype is B–, but black pigment is not produced if the genotype is bb. At an independent locus, gene D produces yellow pigment if the genotype is D–, but no pigment is produced when the genotype is dd. Production of both pigments results in brown coat color. If neither pigment is produced, coat color is cream. Determine the genotypes of parents of litters with the following phenotype distributions. Part A 4 brown, 4 black, 4 yellow, 4 cream

Bbdd and bbDd

Explanation:

From the illustration:

B_dd - black color

bbD_ - yellow color

B_D_ - brown color

bbdd - cream color

In order to produce litters in the ratio 4 brown, 4 black, 4 yellow, and 4 cream; the genotypes of the parents must be Bbdd and bbDd. The cross between the two parents would be such that:

      Bbdd    x    bbDd

4 BbDd - brown color

4 bbDd - yellow color

4 Bbdd - black color

4 bbdd - cream color

See the attached image for the Punnet's square analysis of the cross.

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