Question

A certain species of rabbit can have either black or grey fur. The allele for black fur is dominant over the allele for grey fur. If a homozygous black rabbit is crossed with a heterozygous black rabbit, what phenotypic ratio will occur in the first generation?

A.
50% black : 50% grey
B.
100% black : 0% grey
C.
75% black : 25% grey
D.
25% black : 75

Answer 1

The answer is; B

If we assume that the allele for black fur is B and that for white fur is b, crossing a homozygous black rabbit with a heterozygous black rabbit, will yield the following results (indicated in the punnet square below);

Genotypically, 50% of the population will be homozygous dominant, while 50% will be heterozygous. However, phenotypically, all offspring will bear black fur because the black fur allele is dominant over the grey allele.

Answer 2

B. 100% black : 0% grey

Step-by-step explanation:

If allele for black fur (BB) is dominant over grey fur (bb) and the rabbits can have either of these two colors phenotypically then a cross between a homozygous black rabbit (BB) and heterozygous black rabbit (Bb) will produce all the rabbits with black phenotype.

The cross is shown as under :

Parental BB x Bb

F1 BB BB Bb Bb

Genotypic ratio => BB : Bb = 1:1 i.e. 50% homozygous dominants & 50% heterozygous dominants.

Phenotype will be 100% black rabbits and 0% grey rabbits.