Question

A person with blood type AB has the alleles IA and IB. A person with blood type O has the alleles ii. Why is it impossible for a person with blood type AB to have a child with blood type O?

: A person with blood type AB will give that same blood type to the child.

: The child can have O blood if he gets the ii genotype from the other parent.

: A child with blood type O has to have two different alleles for this blood type.

: A person with blood type AB will give a child either the IA or IB allele.

Answer 1

It is impossible because the IA and IB are dominant alleles therefore always masking the recessive ii alleles for O blood type. The only way for a recessive trait to appear is if both parents at least are a carrier of said recessive allele.