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

Determine the number of possible phenotypes in the $ABO$ blood grouping system.

$A$ 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?

$A$ 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.

Which of the following is an example of multiple allelism?

The blood group of the father is $A$ and the blood group of the mother is $B$. Predict the possible blood groups of the progeny.