Can AB mom have a child A with the father o?

Yes, it is possible for AB mom to have a child A with the father o. This can happen if the mother has a mutation in the ABO gene, which determines blood type. The ABO gene has three alleles: A, B, and O. A person with type A blood has two A alleles, a person with type B blood has two B alleles, and a person with type O blood has two O alleles.

If the mother has an A allele and an O allele, and the father has an O allele, then there is a 50% chance that their child will have type A blood and a 50% chance that their child will have type O blood. This is because the child will inherit one allele from each parent, and there is an equal chance that the child will inherit the A allele or the O allele from the mother.