Question

First husband of ‘X’ had A blood group and their child had an O blood group. She remarried and her second husband had B blood group and their child had AB blood group. What is the ABO genotype of ‘X’ and her blood type?

• A. ii, blood type O
• B. $I^{B}i$, blood type B
• C. $I^A{I}^B$, blood type AB
• D. $I^{A}i$, blood type A

Answer 1

The correct option is D $I^{A}i$, blood type A

The child from the first marriage had O blood group, i.e., the child had $ii$ genotype. So, each one of the alleles of the genotype $ii$ would come from each of the parents. That means both parents had "$i$" in their genotype. Therefore, the genotype of X is $I^{A}i$. The cross is shown below:

Gametes	$I^A$	$i$
$I^B$	$I^A{I}^B$ (AB blood group)	$I^{B}i$ (B blood group)
$i$	$I^{A}i$ (A blood group)	$ii$ (O blood group)

2nd marriage:
B blood group (husband) X A blood group (wife)
$\downarrow$
AB blood group (child)

The child after second marriage had AB blood group. But the husband is B type blood. Hence, "X" (wife) will have A type blood group.

So, the mother has a genotype $I^{A}i$.