Olga has blood group B and is heterozygous. Phillimon has blood group A and is homozygous. What are the possible blood groups of their children?

Olga has blood group B and is heterozygous. The genotype for heterozygous blood group B is $I^B i$.
Phillimon has blood group A and is homozygous. The genotype for homozygous blood group A is $I^A I^A$.

The gametes from Olga are $I^B$ and $i$.
The gametes from Phillimon are $I^A$ and $I^A$.

From the Punnett square, the possible genotypes are $I^A I^B$ and $I^A i$.

• Genotype $I^A I^B$ results in blood group AB (due to codominance).
• Genotype $I^A i$ results in blood group A (since $I^A$ is dominant over $i$).

The possible blood groups of their children are AB and A.

The possible blood groups of their children are:

• Blood group AB
• Blood group A