Question

A woman is married for the second time. Her first husband was blood type A and her child by that marriage was type O. Her new husband is type B and their child is type AB. What is the women’s ABO genotype and blood type?

• A. $I^A{I}^O$; Blood type A
• B. $I^A{I}^B$; Blood type AB
• C. $I^B{I}^O$; Blood type B
• D. $I^O{I}^O$; Blood type O

Answer 1

The correct option is A $I^A{I}^O$; Blood type A

Blood groups are inherited from our biological parents in the same way as eye colour and other genetic traits. Within the ABO blood group system, the A and B genes are co dominant, i.e., these will be expressed whenever the gene is present. The O gene is silent and only expressed when neither A nor B is present.

In the first marriage, the child is blood group O, $I^O{I}^O$ which means both the parents have $I^O$ alleles. In the second marriage, the child has AB blood type. In this case, the father has B type, either $I^B{I}^O$ or $I^B{I}^B$. This means the mother has A type blood with genotype $I^A{I}^O$.