Inheritance of $ABO$ blood group system is an example of

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.

The offspring produced from a marriage have only $O$ or $A$ blood groups. Of the genotypes given below,the possible genotypes of the parents would be

$A$ child with a mother of $O$ blood group and a father of $A$ blood group will have which of the following blood groups?

$A$ man of blood group-$A$ marries a woman of blood group-$B$. Both of them are heterozygous for their blood group. The chances of their first child having blood group $AB$ will be: (in $, \%$)