If a man has type A blood, but his mom had type O blood, what must be his genotype? IAIA IAi ii

IAi

Explanation:

The genotype for O blood is ii. So his mom must have given him an i allele. So he has at least one i allele.

But since his phenotype is A -- he expresses A -- there must be one IA allele. Otherwise, if he had both ii, he would be an O-type blood.

So his genotype must be IAi.

just go with your heart buddy