Question

Write a note on multiple alleles considering examples of human blood groups.

Answer 1

1. More than two alternative forms (alleles) of a gene in a population occupying the same locus on a chromosome or its homologue are known as multiple alleles.
2. ABO blood group system in humans is an example of multiple allelism because gene I exists in three allelic forms I^A, I^B and I^O.
3. Here, allele I^A codes for type A blood, allele I^B codes for type B blood and allele I^O codes for type O blood.
4. Allele I^O is recessive to the alleles I^A and I^B.
5. Thus, with these three alleles, we can have 6 different genotypes and 4 different phenotypes for blood groups.

	Genotype	Phenotype (Blood group)
1.	IA IA or IA IO	Type A
2.	IB IB or IB IO	Type B
3.	IA IB	Type AB
4.	IO IO	Type O