Question

Bert has blonde hair (b). Molly has brown hair (B), but her genotype is Bb, meaning she carries a recessive blonde allele.

What is the likelihood of Bert and Molly's second child having brown hair?

• 25%

• 75%

• 50%

• 100%

Answer 1

There are two alleles for the hair colour.

Dominant allele, B = Brown hair

Recessive allele, b = blonde hair

Bert has blonde hair. So his Genotype is bb.

Molly has brown hair but is Heterozygous. So her Genotype is Bb.

Parents :- bb × Bb

Gametes :- b & b × B & b

Offsprings :-

Punnett square

Male⬇️/ Female ➡️	B	b
b	Bb	bb
b	Bb	bb

The offsprings can either brown hairs or blonde hairs.

The ratio of brown hair to blonde hair = 1:1

Both the genotypic and phenotypic ratio is 1:1

So any child is having probability of 50% to have either of these hair colours.

Thus the probability of Bert and Molly's second child having brown hair is 50%.

The correct answer is (c) 50%