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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, blonde hair
bb, blonde hair

BB, brown hair
BB, brown hair

Bb, brown hair
Bb, brown hair

Bb, blonde hair
Bb, blonde hair
Re

1 answer

To solve this problem, we need to determine the genotype of the other parent based on the children produced.

  1. The first child has blonde hair (bb). This means that both alleles inherited from the parents must be recessive (b). To have a child with blonde hair, one parent must contribute a recessive allele (b).

  2. The second child has brown hair (BB). This means that the child received a dominant allele (B) from both parents.

From the information given, we know:

  • The brown-haired parent (Bb) can pass on either a B or a b.
  • The child with blonde hair must have inherited a b from both parents. Therefore, the other parent must also have contributed a recessive allele (b).

Given that the brown-haired parent (Bb) can give either B or b, the other parent must have at least one recessive allele (b) to produce a blond child. However, since the second child has brown hair, the other parent can either be homozygous dominant (BB) or heterozygous (Bb).

  1. If the other parent is bb, they can only provide b alleles, which is consistent because they contributed b for the first child.
  2. If the other parent is BB, they cannot contribute any b alleles, which would not produce the blonde-haired child.

Thus, the only combination that fits all conditions stated is:

Bb, brown hair.

This means the other parent has brown hair but is a carrier of the blonde hair allele (b).