Question

Explain the phenomena of multiple allelism and co-dominance taking ABO blood group as an example.

Answer 1

One gene I has three alleles I^A,  I^B and i hence multiple allelism. We inherit any two of them. When the genotype is   I^A I^B, the individual has AB blood group since both I^A and I^B equally influence the formation of Antigen A and B- Co-dominance.

Detailed Answer : 

(a) Multiple allelism is the phenomenon of occurrence of a gene in more than two allelic forms on the same locus homologous pair chromosome. In ABO blood group in humans one gene I has three alleles I^A, I^B and i. 

Co-dominance is the phenomena in which both alleles of a gene express themselves when present together. We inherit any two of the three alleles for the blood group. When the genotype is I^AI^B the individual has AB blood group since both I^A and I^B equally influence the formation of antigens A and B.