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

If a child has $O$ type of blood group and the father has $B$ type,the genotype of the father will be:

If the mother's blood group is $AB$ and the father's blood group is $O$,what will be the possible blood group$(s)$ of the child?

Mother is homozygous for blood group $B$,and father has blood group $A$ (genotype unknown). Therefore,the possible blood groups in the progeny are:

In humans,the $ABO$ blood group is controlled by the $I$ gene. It has three alleles: $I^A$,$I^B$,and $i$. Although there are three different alleles,six different genotypes are possible. How many phenotypes are observed in this case?

If one parent has blood group $A$ and the other has blood group $B$,what blood group$(s)$ can their offspring have?