Question

A woman of blood group 'O' presented a baby girl of blood group 'O' which she claimed as her child. She brought a sue against a man of 'AB' blood group as the father of the child. Which statement is correct as per your judgement?

• A. Father and mother claimed are the true persons.
• B. Man is the father but the woman is not the mother of the child.
• C. Both the parent's claims are false.
• D. The women is the mother but the man is not the father of the child.

Answer 1

The correct option is D The women is the mother but the man is not the father of the child.

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 mother and daughter are of blood type O (I${}^O$ I${}^O$) and the suspected father has AB blood group (I${}^A$ I${}^B$).
Parent generation : I${}^A$ I${}^B$ x I${}^O$ I${}^O$

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

F${}_1$ generation phenotypic ratio = 2 A group : 2 B group; hence parents with AB and O blood group can not have a child with O blood group. Further, to have a daughter with 'O' blood group, both parents must have at least one I${}^O$ allele to transmit it to the daughter. Mother has two'I${}^O$' alleles but father has none; hence he cannot be the father of the daughter.

Thus, the correct answer is option D.