If two black mice are crossed, the resulting offspring are as follow: 10 black mice and 3 white, what are the genotype of the parents?

Bb and Bb

Explanation:

Let B be the allele of a black color;  &

Let b be the allele of a white color

Allele B is dominant over allele b, and as such it masks the expression of allele b

If we have a cross between two heterozygous individuals

i.e Bb × Bb

we have:

               B                b

B              BB             Bb

b              Bb              bb

From above, Phenotypically;

we have the following offspring:

BB  ;   one normal black color

2 Bb:  two heterozygous for black color

bb : one white color

The color ratio is in the ratio of 3 black :1 white  which is synonymous to 10 black : 3 white

So; we can therefore conclude that the genotype of the parents are :

Bb and Bb

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