On which chromosome are the genes for the $ABO$ blood group located?

If the father has $AB$ blood group and mother has $A$ blood group,then the children born to them will have the following blood groups $EXCEPT$ . . . . . . .

$A$ male with heterozygous blood group $B$ and a female with homozygous blood group $A$ have offspring. What are the possible genotypes and phenotypes in their progeny?

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?

$A$ pair of contrasting characters is termed as

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