Self-sterility in $Nicotiana$ was reported by:

In a marriage between a male with blood group $A$ and a female with blood group $B$,the progeny had either blood group $AB$ or $B$. What could be the possible genotype of parents?

$A$ 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 of $O$ blood group has a $B$ blood group father. The genotype of the father will be:

$A$ 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 $, \%$)

$ABO$ blood grouping is an example of: