Question

Three children of a family have blood groups A, AB and B. What could be the genotypes of their parents?

• A. $I^{A}i$ and $I^{B}i$
• B. $I^A{I}^B$ and i i
• C. $I^B{I}^B$ and $I^A{I}^A$
• D. $I^A{I}^A$ and i i
• E. None of the above

Answer 1

Answer: (A)

Human blood group inheritance is governed by three alleles namely I${}^A$, I${}^B$ and i. I${}^A$ and I${}^B$ show codominance while allele "i" is recessive to both "I${}^A$" and "I${}^B$". Therefore, children with A blood group have atleast one I${}^A$ allele but no I${}^B$ allele while those with B blood group have atleast one I${}^B$ allele but no I${}^A$ allele. Similarly, children with AB blood group will have one copy of each I${}^A$ and I${}^B$ allele. Option A is correct as the children with A, B and AB blood group are produced. Another child with O blood group can be produced along with these children as there is presence of i allele in both parents.

Thus, the correct answer is option A.