Can a child have blood group O if his parents have blood group 'A' and 'B'. Explain.

Genotype and phenotype of blood groups
Phenotype Genotype

A	I${}^A$ I${}^A$ (Homozygous) and I${}^A$I${}^O$ (Heterozygous)
B	I${}^B$I${}^B$ (Homozygous) and I${}^B$I${}^O$ (Heterozygous)
AB	I${}^A$I${}^B$ (Heterozygous)
O	I${}^O$I${}^O$ (Homozygous)

Possibility of child with 'O' blood group if parents have 'A' and 'B' blood groups

Possibility of a child with 'O' blood group if parents have 'A' and 'B' blood groups is dependent on the alleles of 'I' gene present in parents.

When the parents have I${}^A$ I${}^O$ (Heterozygous) and I${}^B$ I${}^O$ (Heterozygous) genotypes, they will have blood group A and B respectively. This is because I${}^A$ and I${}^B$ are dominant over I${}^O$.

If the recessive allele 'I${}^O$' is passed to the offspring from both the parents, then the child will have O blood group.