Pattern baldness in humans is a sex-influenced trait that is autosomal dominant

Question

Pattern baldness in humans is a sex-influenced trait that is autosomal dominant in males and recessive in females. Jack is bald, his mother had a full head of hair. Jo Ann has a full head of hair, but her mother was bald. What proportion of Jack and JoAnn’s children are expected to be bald?

a.

all males will be bald : all females will have full hair

b.

all males will be bald : 1/4 females will be bald

c.

1/2 males will be bald : 1/2 females will be bald

d.

1/4 males will be bald : 3/4 females will be bald

e.

3/4 males will be bald : 1/4 females will be bald

Explanation / Answer

Let the alleles be denoted as,

BB(homozygous dominant), Bb(heterozygous dominant), bb(homozygous recessive)

The baldness is autosomal dominant in males and recessive in females.

Jack's mother has full head of hair, her genotype could be either BB or Bb and Jack's genotype will be Bb.

Jo Ann's mother is bald so her genotype is bb(recessive) but she has full head of hair so her genotype should be Bb.

Jack x Jo Ann = Bb x Bb

The possible genotypes will be BB, Bb, Bb and bb.

3/4 males will be bald and 1/4 female will be bald.

So the answer is e.

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