Explain multiple alleles with respect to ABO blood group in humans

An allele is a variant or alternate form of gene which are found on same gene loci. Humans are diploid organisms having two alleles for a given gene. However in nature more than two variants are possible. One such example is multiple alleles in human ABO blood group. The blood groups known are A, B, O and AB which are determined by a single gene 'I'. having three alleles. The allelic forms are represented as IA, IB and Io for A, B and O antigen respectively. There are 6 possible genotypic combinations resulting in the four blood groups determined by the presence of the two inherited alleles.Now, IA, IB are codominant that is in the presence of each other both antigens are expressed where as Io is recessive to both (i.e expressed only in homozygous condition).
IAIA IA Io - results in blood type AIBIB IB Io - Results in blood type BIAIB - Results in blood type ABIo Io - results in blood type O

Answered by Hamsika K. Biology tutor

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