Question

In a family, father has a blood group A and mother has a blood group B. Their children show 50% probability for a blood group AB indicating that

• A. Father is heterozygous
• B. Mother is heterozygous
• C. Either of parent is heterozygous
• D. Mother is homozygous

Answer 1

Answer: (C)

Either of parent is heterozygous

Genotype of a child with AB blood group is I${}^A$I${}^B$. A parent with A blood group can have two possible genotypes: I${}^A$I${}^A$ and I${}^A$I${}^O$, similarly parent with B blood group can have two possible genotypes: I${}^B$I${}^B$ and I${}^B$I${}^O$. If both the parents are homozygous (I${}^A$I${}^A$ x I${}^B$I${}^B$), all of their children will have AB blood group. But, if father is heterozygous (I${}^A$I${}^O$) and mother is homozygous (I${}^A$I${}^A$); the total different types of possible combinations by three allele (I${}^A$, I${}^B$ and I${}^O$) will be (I${}^A$I${}^B$ and I${}^B$I${}^O$). Thus, their children show 50% probability for a blood group AB. But, if mother is heterozygous (I${}^B$I${}^O$) and father is homozygous (I${}^A$I${}^A$), the total different types of possible combinations by three allele (I${}^A$, I${}^B$ and I${}^O$) will be (I${}^A$I${}^B$ and I${}^B$I${}^O$. Thus, their children also show 50% probability for a blood group AB. This means that 50% probability for blood group 'AB' children from father with A and mother with blood group B indicates that either of the parent is heterozygous.

Thus, the correct answer is option C.