Question

A child of O blood group was born to a mother of blood group A and father of blood group B. What are the genotypes of parents?

• A. Mother----$I^A{I}^A$, Father----$I^B{I}^B$
• B. Mother----$I^A{I}^O$, Father----$I^B{I}^O$
• C. Mother----$I^B{I}^B$, Father----$I^A{I}^A$
• D. Mother----$I^B{I}^O$, Father----$I^A{I}^O$

Answer 1

Answer: (B)

Mother----$I^A{I}^O$, Father----$I^B{I}^O$

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 IBIO 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.

Therefore, the correct answer is option B.