Question

The possible blood groups of the offspring of the parents with blood group O and AB are

• A. O, A, B and AB
• B. A, B and AB
• C. A and B
• D. O and AB

Answer 1

Answer: (C)

A and B

The IA allele gives type A, IB gives type B, and IO gives type O. As both, IA and IB are dominant over IO, only IO/IO people have type O blood. Individuals with IA/IA or IA/IO have type A blood and individuals with IB/IB or IB/IO have type B. IA/IB people have both phenotypes because A and B express a special dominance relationship: codominance, which means that type A and B parents can have an AB child. A couple with type A and type B can also have a type O child if they are both heterozygous (IB/IO, IA/IO). So, the possible blood groups of the offspring of the parents with blood group O and AB are A and B because their parents' genotypes are IO/IO and IA/IB. So, under crossing, we get only A and B blood groups.

Therefore, the correct answer is option C.