Some mutations occur at the same locus of a chromosome. They produce ..........

$A$ 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?

In humans,how many genotypes and phenotypes are produced by the three different alleles of the $ABO$ blood group system?

$A$ man with blood group $AB$ marries a woman with $O$ blood group. In this situation,

$ABO$ blood grouping in humans is controlled by the gene $I$. It has three alleles: $I^A, I^B,$ and $i$. Due to these three different alleles,six different genotypes are possible. How many phenotypes can be formed from these?

Where are multiple alleles found?