Question

In rabbits, black fur (B) is dominant to brown fur (b).

Answer 1

1. Heterozygous black rabbit will have genotype Bb

2. If a heterozygous black rabbit and a brown rabbit were crossed:

Bb  x bb

The offspring will be:

Bb Bb bb bb

Which means that half of them will be black and half brown (50%).

Answer 2

Answer:

1. Bb

2. 1/2

Explanation:

The cross in this question involves a single gene that codes for fur colour in rabbits. According to the question, black fur is dominant to brown fur. This means that the allele for black fur (B) will mask the expression of brown fur allele (b) in the gene.

1. HETEROZYGOUS means that the organism contains a combination of the two different alleles (black and brown alleles in this case). Hence, the genotype of a rabbit heterozygous for this gene will be Bb. Since black allele (B) is dominant over brown allele (b), the black fur colour will be expressed phenotypically.

2. In a cross between a heterozygous black rabbit (Bb) and a brown rabbit. Note that, the brown rabbit will have a homozygous genotype (bb) since it will only be expressed in a homozygous state. Hence, rabbit parents Bb and bb will be crossed to produce four possible offsprings viz: Bb, Bb, bb and bb

Two of the offsprings are heterozygous black while the other two are brown. Hence, the probability that their offspring will be brown is 2/4 equivalent to 1/2