4. What genotypes of parents will have only white-fur offspring? Parent 1 genotype = Parent 2 genotype = What genotypes of parents will have only black-fur offspring? Parent 1 genotype = Parent 2 genotype =

All white offspring: Parent 1 genotype = homozygous dominant

                            Parent 2 genotype = homozygous/heterozygous dominant

For all black offspring: Parent 1 genotype = homozygous recessive

                                     Parent 2 genotype = homozygous recessive

Explanation:

The cross was between a white mouse and a black mouse and the phenotypic ratio of the resulting offspring is 50% white and 50% black.

Assuming that fur color in the mouse is represented by the allele A (a), In order to give 1:1 phenotypic ratio of the offspring, it means the white mouse is heterozygous with Aa genotype and the black mouse is homozygous with aa genotype. Also, it means that the allele A is dominant over the allele a.

                       Aa    x    aa

                 Aa    Aa    aa    aa

Aa = white

aa = black

Ratio of white to black = 50/50 or 1:1

Hence, in order for a cross to yield only white offspring, the parents can either be homozygous AA and AA or one will be homozygous AA and the other will be heterozygous Aa.

1.              AA    x    AA

       AA    AA    AA    AA (all white offspring)

2.            AA    x    Aa

        AA    Aa    AA    Aa (all white offspring).

In order to produce only black offspring, both parents must be homozygous aa.

             aa    x    aa

         aa    aa    aa    aa    (all black offspring)

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