$ABO$ blood grouping is controlled by gene $I$,which has three alleles and shows co-dominance. There are six genotypes. How many phenotypes in all are possible?

If the father has $AB$ blood group and mother has $A$ blood group,then the children born to them will have the following blood groups $EXCEPT$ . . . . . . .

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?

$A$ pair of contrasting characters is termed as

$A$ man with blood group $A$ marries a woman having blood group $B$. The maximum possible blood groups among their progenies are

$A$ child has blood group $O$. If the father has blood group $A$ and mother has blood group $B$,work out the genotypes of the parents and the possible genotypes of the other offspring.