Genetics problem?

Question

Genetics problem?
I'm usually opposed to ppl who post their homework on here, but I'm stuck on this problem:

A father of a certain family belongs to blood group AB, and the mother belongs to blood group O. They have four children, one belonging AB, one to group A, one to group B, and one to O. One of these children is adopted and another child is from an earlier marriage of the mother. State whih is the adopted child and which is the child from an earlier marriage.

Answer 1

This is easy. I am an MD. A person will inherit either one antigen (A or B) or no antigen (blood group O) from each parent. Since the mother is type O, it is absolutely impossible for her to bear a child of blood group AB. Therefore, any children that she may have of this blood type MUST be adopted. Furthermore, the father of blood type AB MUST transmit either an A or a B to each and every one of his offspring. He simply cannot father a type O child. Therefore, any type O children that he may have MUST be adopted, or else fathered by a different man, (the handsome mailman of blood type O maybe?) I hope this helps.

Answer 2

The AB kid was adopted. The O type kid was from mother's previous marriage.

Reasoning: The current father is AB and the mom is O. O is recessive to both A and B blood types. When haploid gametes form in the father, one will have only A and the other only B but NEVER AB. Since the mom's gametes are all O, the children from this marriage can only have A or B blood type. NEVER AB and NEVER O.
The O child could have only come from previous husband who also was O.
To get an AB child, The father can be AB, but the mother would need to be an A or B type, not O.

Answer 3

The only possible children's blood types from the current marriage would be AO (Type A) or BO (Type B). The child with type AB blood must be the adopted child because the mother does not possess either the A or B allele. The child with type O blood is from the mother's previous relationship because Type O matches her genotype, but not the current father's.