Multiple alleles are present:

1. on different chromosomes
2. at different loci on the same chromosome
3. at the same locus of the chromosome
4. on non-sister chromatids

A man with blood group 'A' marries a woman with blood group 'B'. What are all the possible blood groups of their offspring?

ABO blood groups in humans are controlled by the gene I. It has three alleles – I^A I^B and i. Since there are three different alleles, six different genotypes are possible. How many phenotypes can occur?

1. Three

2. One

3. Four

4. Two

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?