Question

When both parents are of blood type AB, they can have children with

• A. A, B, AB and O blood types
• B. A, B and AB blood types
• C. A and B blood types
• D. A, B and O blood types
• E. A, AB and O blood types

Answer 1

Answer: (B)

A, B and AB blood types

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${}^B$. This gives total six genotypes and four phenotypes - A (I${}^A$ I${}^A$ and I${}^A$ I${}^O$), B (I${}^B$ I${}^B$ and I${}^B$ I${}^O$), AB (I${}^A$ I${}^B$) and O (I${}^O$ I${}^O$). Both parents are of blood type AB.
Parent generation : I${}^A$ I${}^B$ x I${}^A$ I${}^B$

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

F${}_1$ generation phenotypic ratio = 1 A group : 2 AB group : 1 B group; hence, parents with AB blood group can have a child with A, AB and B blood group. Correct option is "B".