What are the products of the $I^A$ and $I^B$ alleles?

The offspring produced from a marriage have only $O$ or $A$ blood groups. Of the genotypes given below,the possible genotypes of the parents would be

$A$ man with blood group $AB$ marries a woman with $O$ blood group. In this situation,

On which chromosome are the genes for the $ABO$ blood group located?

$ABO$ blood groups are controlled by the gene:

Considering the concept of multiple alleles,one individual can have only . . . . . . alleles for that character.