$ABO$ blood grouping is controlled by gene $I$,which has three alleles and shows co-dominance. There are six genotypes. How many phenotypes in all are possible?

What does a gamete contain in a multiple allele system?

The $ABO$ blood group is controlled by:

The plasma membrane of the red blood cells has ...$A$... polymers that protrude from its surface and the kind of sugar is controlled by the gene. The gene $I$ has three alleles ...$B$... The alleles and produce a slightly different form of the sugars,while allele $i$ doesn't produce any ...$C$...
Choose the correct option for $A, B$ and $C$.

If the mother's blood group is '$A$' and the father's blood group is '$AB$',then the possible blood groups of their children will be:

The number of phenotypes in $ABO$ blood group is