Can a son have type A blood and his dad O?

Yes, a son can have type A blood even if his dad has type O blood. This is because the son may have inherited the A allele from his mother. A person's blood type is determined by the combination of two alleles, one inherited from each parent. The A and B alleles are dominant, while the O allele is recessive. If a person has one A allele and one O allele, they will have type A blood.

This is because the A allele will be expressed, while the O allele will not. Therefore, if a man with type O blood (OO) has a child with a woman who has type A blood (AO or AA), there is a possibility that the child will inherit the A allele from the mother and have type A blood, while the father can only donate the O allele to the child.