Question

Parents of blood groups O and AB cannot have a child of group AB because

• A. Gene O is dominant over gene A
• B. Gene O is dominant over gene B
• C. Gene A and B are absent in one of the parents
  
• D. None of the above

Answer 1

Answer: (C)

Gene A and B are absent in one of the parents

Heterozygous IA/IB individual have blood group AB. Both the A antigen (product of the IA alleles) and the B antigen (product of the IB alleles) are produced by them. So, parents of blood groups O and AB cannot have a child of group AB because gene A and B are absent in one of the parents.