Question

The possible blood groups of children born to parents having A and AB groups are

• A. O, A
• B. A, B, AB
• C. O, A, B
• D. O, A, B, AB

Answer 1

The correct option is B A, B, AB

Human blood group inheritance is the example of codominance and multiple alleles. It is governed by three alleles namely I${}^A$, I${}^B$ and I${}^O$. I${}^A$ and I${}^B$ show codominance while allele I${}^O$ is recessive to both I${}^A$ and I${}^B$.

The genotype of a person with “A” blood group can be I${}^A$I${}^O$ or I${}^A$I${}^A$ and that of the parent with AB blood group is I${}^A$I${}^B$. The alleles I${}^A$, I${}^O$ and I${}^B$ can make three genotypic combinations, namely I${}^A$I${}^A$, I${}^A$I${}^O$, I${}^A$I${}^B$ and I${}^B$I${}^O$. Thus, the possible blood group of their children is A, B and AB. To have a child with O blood group, both parent should have at least one I${}^O$ allele; thus they can’t have a child with O blood group.
Cross 1
Parent generation : I${}^A$ I${}^A$ x (I${}^A$ I${}^B$)

Gametes : I${}^A$ I${}^A$--> (I${}^A$ I${}^B$)	I${}^A$	I${}^A$
I${}^A$	I${}^A$I${}^A$	I${}^A$I${}^A$
I${}^B$	I${}^A$I${}^B$	I${}^A$I${}^B$

F${}_1$ generation phenotypic ratio = 1 A group : 1 AB group

Cross 2
Parent generation : I${}^A$ I${}^O$ x (I${}^A$ I${}^B$)

Gametes : I${}^A$ I${}^O$ --> (I${}^A$ I${}^B$)	I${}^A$	I${}^O$
I${}^A$	I${}^A$I${}^A$	I${}^A$ I${}^O$
I${}^B$	I${}^A$I${}^B$	I${}^B$ I${}^O$

F${}_1$ generation phenotypic ratio = 2 A group : 1 AB group : 1 B group