6.

Question

A child has sickle-cell disease ( ss ) but neither parent is ill. What must be true of her parents’ genotypes?

One parent has two recessive alleles.

The father is heterozygous; the mother is normal.

The mother is heterozygous; the father is normal.

Both parents are heterozygous carriers.

Answer 1

Both parents must be heterozygous carriers (Ss).