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

(b) What is the phenotype of the following:

(i) I^Ai

(ii) ii

a. The blood groups in humans are controlled by the gene I which exist in three allelic forms ‘i’, ‘I^A’, and ‘I^B’. Thus, it shows multiple allelism i.e., a phenomenon where a gene exists in more than two allelic forms.

I^A, and I^B codes for glycoprotein that protrudes from the surface of the RBCs while ‘i’ does not code for anything. Therefore I^A, and I^B are codominant over each other i.e., two alleles of a gene are not dominant over each other and express themselves independent of each other.

b.

i. The phenotype of I^Ai is A blood group

ii. The phenotype of ii is O blood group