Species in which dark brown fur (D) is dominant relative to light brown fur (d). Using the Punnett square below, predict the frequencies of the genotypes and phenotypes of the offspring from dark brown parents two who are heterozygous (Dd genotypes).

25% DD

50% Dd

25% dd

or

1 DD: 2 Dd: 1 dd

75% Dark brown, 25% light brown

or 3 dark brown: 1 light brown

Explanation:

Two heterozygous parents have the genotypes Dd. Therefore, the cross is Dd x Dd.

           D                   d

D        DD                 Dd

d        Dd                  dd

25% (1:4) of the organisms have the genotype DD, and therefore the phenotype is dark brown,  since it has two copies of the dark brown fur allele (DD)

50% (1:2) of the organisms have the genotype Dd, and therefore, the phenotype is dark brown since dark brown fur (D) is dominant to light brown  fur (d).

25% (1:4) of the organisms have the genotype dd, and therefore the phenotype is light brown, since it has two copies of the light brown fur allele (DD)

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