Can a baby born with type AB blood belong to dad that has A and mom O?

Yes, it is possible for a baby to be born with AB blood if the father has A and the mother has O blood. This is because of a genetic phenomenon known as codominance.

When a person has type A blood, they have two alleles for the A blood type antigen on their red blood cells. When a person has type O blood, they have two alleles for the O blood type antigen.

When a person with A blood and a person with O blood have a child, the child can inherit either the A or the O allele from each parent. If the child inherits the A allele from the father and the O allele from the mother, they will have type A blood. However, if the child inherits the A allele from the mother and the O allele from the father, they will have type B blood.

In some cases, a child may inherit one A allele and one O allele from their parents. This is called the codominant inheritance. In this case, the child's red blood cells will express both the A and O antigens, resulting in type AB blood.