Question

A woman of blood group ‘O’ presented a baby girl of blood group ‘O’ which she claimed as her child. She brought a suit 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 parents’ claims are false
D) The woman is the mother, but the man is not the father of the child.

Answer 1

Blood type is an inherited trait, and like many genetic traits, the ABO blood typing system is controlled by dominant and recessive genes. The A and B genes are codominant, while the O gene is recessive.

Complete answer:

If the woman is blood group O, it means she is homozygous recessive for O. In order for her to have a child of blood group O, the father has to be one of three blood types: AO, BO, or OO. The man cannot be the father, though the woman can be the mother. Option A is incorrect.
A parent with AB blood group has the co-dominant genes A and B. If this person parents a child with someone of blood type O, the child would genotypically be AO or BO, and phenotypically be type A or Type B. The man cannot be the father. Option B is incorrect.
A woman with type O can have a child of type O if the father was O or carried heterozygous. So her claim to be the mother is correct. Option C is not the answer.
In this scenario, of the mother being type O, and the child being type O, it is genetically not possible for the man of type AB to be the father of this child. Option D is therefore the correct answer.

Hence the correct answer is option ‘D’.

Note: Along with the ABO system of blood grouping, the Rh factor is also very important. Any of the ABO blood groups can be $Rh^+$ or $Rh^-$. This is very important when blood transfusions are being given as the recipient could die.