Explain the genetic basis of blood grouping in human population

Human blood group inheritance is the example of codominance and multiple alleles. It is governed by three alleles namely IA, IB and i. IA and IB show codominance while allele "i" is recessive to both "IA" and "IB". This gives total six genotypes and four phenotypes- A (IAIA and IAi), B (IBIB and IBi), AB (IAIB) and O (ii).