Multiple alleles are present:

$A$ couple has four children with blood groups $A, AB, A,$ and $O$ respectively. What are the genotypes of the parents' blood groups?

If the blood group of the mother is $A$ and the blood group of the father is $O$,what may be the blood group of the progeny?

$ABO$ 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?

How many phenotypes and genotypes are possible in $ABO$ blood group systems?

If a man with blood group $A$ marries a woman with blood group $AB$,which of the following offspring would indicate that the man is heterozygous for blood group $A$?