Question

Considering a condition in which a mother has blood group O, father has blood group A and the child being group B, which of the following statements is correct?

• A. The mother may have $I^B$ allele that is passed to the child
• B. The father of the child maybe someone else with B or AB blood type
• C. The child has $I^A$ allele and also $I^B$ allele
• D. This is a normal case

Answer 1

The correct option is B The father of the child maybe someone else with B or AB blood type

A child having B blood group should have allele $I^B$. Since the mother is having O blood group she should be homozygous $I^O{I}^O$ and father having a A blood group will be either hetrozygous dominant or homozygous dominant i.e., $I^A{I}^O$ Or $I^A{I}^A$

Clearly in case I, the blood group of the child is A (50%) or O (50%). In case II the offspring blood group is clearly A. No case of the child's blood group being any other is observed.

So it is evident that the paternity of the child is in question, and the male parent is not the biological father of the child. The biological father has an $I^B$ allele. Thus, the father of the child maybe somone else with either B ($I^B{I}^B\mathrm{or}{I}^B{I}^O$) or AB ( $I^A{I}^B$) blood group.

Case I

Case II