Which of the following characteristics can be expressed by $3$ alleles?

In humans,four phenotypes of blood groups are due to the presence of antigen-$A$ and antigen-$B$ on the $RBC$. The chromosome that carries the gene controlling these antigens is:

Sometimes,there are more than two alleles for a given chromosome locus. In this case,a trait is said to be governed by:

If both parents have blood group $AB$, which blood group cannot be found in their child?

$A$ man with blood group $B$ marries a woman with blood group $A$ and their first child has blood group $B$. What is the genotype of the child?

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