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Blonde hair (b) is recessive, and brown hair (B) is dominant.

A parent has brown hair (Bb). Their first child has blonde hair (bb). Their second child has brown hair (BB).

What must the other parent have (hair color and allele combination)?

(1 point)
Responses

Bb, brown hair
Bb, brown hair

BB, brown hair
BB, brown hair

Bb, blonde hair
Bb, blonde hair

bb, blonde hair

1 answer

To determine the hair color and allele combination of the other parent, we need to look at the offspring produced by the parents.

  1. The first child has blonde hair, which has the genotype (bb). This indicates that they received one recessive allele (b) from each parent.
  2. The second child has brown hair with the genotype (BB). This means that they received a dominant allele (B) from each parent.

Since the first child is (bb), the other parent must have contributed a (b) allele. Therefore, the other parent must have at least one (b) allele.

Given that the second child is (BB), this means that the other parent must also have given a (B) allele to the second child. This means that the other parent's genotype must be a combination of both (B) and (b) alleles.

The only possible allele combination for the other parent that satisfies both conditions (contributing a b allele for the blonde-haired child and a B allele for the brown-haired child) is:

Bb, brown hair.

So the correct answer is:

Bb, brown hair.