Question

A man with blood group B marries a woman with blood group A and their first child is having blood group B. What is the genotype of the child?
A. $I^{B}I^{O}$
B. $I^{B}I^{B}$
C. $I^{A}I^{O}$
D. $I^{A}I^{B}$

Answer 1

Blood groups are inherited by our parents the same way as we inherit hair colour, eye colour etc. The ABO blood group is controlled by a single gene called the ABO gene which has multiple alleles.

Complete Answer:
- The alleles of ABO gene are $I^A$, $I^B$, $I^O$. I stand for isoagglutinogen or antigen. The IA allele gives type A, IB allele give type B and $I^O$ allele gives type O. $I^A$ and $I^B$ are dominant over $I^O$.
- IA and IB is an example of codominance. IA and IB are dominant whereas IO is recessive. The genotypes are as follows- A (IAIA, $I^{A}I^{O}$), B ($I^{B}I^{B}$, $I^{B}I^{O}$), AB ($I^{A}I^{B}$) and O ($I^{O}I^{O}$).
- If the mother has A group and father has B, the child receives one allele of B from father and the other from mother A. So the child cannot have IB IB. The child gets the blood group B, the genotype will be $I^{B}I^{O}$.
- $I^{B}I^{B}$ genotype is possible if both the parents are of B group.
- $I^{A}I^{O}$ genotype is possible if the child gets blood group A.
- $I^{A}I^{B}$ genotype is possible if the child has AB blood group.

Thus the correct answer is (A). The genotype of child would be $I^{B}I^{O}$.

Note: Felix Bernstein discovered the correct blood group inheritance pattern of multiple alleles 1924. The blood group inheritance is helpful in paternity testing. A couple of blood groups A and B can also get a child of blood group O if they are heterozygous.