Question

If a man with blood group A marries a woman with blood group O, the possible blood groups of their children would be:

• A. A only
• B. A and O
• C. O only
• D. A, AB and O

Answer 1

The correct option is B A and O

ABO blood groups are controlled by multiple alleles $I^A$, $I^B$ and $I^O$. Out of the three alleles, $I^A$and $I^B$ alleles are dominant and $I^O$ is the recessive allele. $I^A{I}^A$ or $I^A{I}^O$ genotypes code for blood group A, while the blood group O is due to the genotype $I^O{I}^O$.

In the above mentioned case, the genotypes of the father have not been specified, and hence both possible genotypes for the man with blood group A have to be considered. If he is homozygous ($I^A{I}^A$), the couple will have children with A blood group only, but if he is heterozygous ($I^A{I}^O$), the couple could have either A or O blood group children.

If the father is homozygous - $I^A{I}^A$

	$I^A$	$I^A$
$I^O$	$I^A{I}^O$(A group)	$I^A{I}^O$ (A group)
$I^O$	$I^A{I}^O$(A group)	$I^A{I}^O$(A group)

If the father is heterozygous - $I^A{I}^O$

	$I^A$	$I^O$
$I^O$	$I^A{I}^O$ (A group)	$I^O{I}^O$(O group)
$I^O$	$I^A{I}^O$ (A group)	$I^O{I}^O$(O group)