Question

A woman gives birth to a son who has type A blood. She has type AB blood. Which of the following can be concluded from this about her parents' blood types?
One of her parents had at least one A allele and the other at least one B allele.
One of her parents had type AB blood.
One of her parents had type B blood and the other type A blood.
One of her parents had two A alleles.

Answer 1

Answer:

One of her parents had at least one A allele and the other at least one B allele.

Explanation:

ABO blood group is regulated by gene "I" with three alleles: I^A, I^B and i. Since alleles I^A and I^B are codominant over each other, genotype I^A I^B gives "AB" blood type. The genotype of woman with AB blood type is "I^A I^B" which means that she has received one A allele from one parent and one B allele from other parent. Therefore, one of her parents had at least one A allele and the other at least one B allele.

Answer 2

One of her parents had type B blood and the other type A blood.