Question

(a) Why is human ABO blood group gene considered a good examples of multiple alleles?
(b) Work out a cross up to $F_1$ generation only, between a mother with blood group A (Homozygous) and the father with blood group B (Homozygous). Explain the pattern of inheritance exhibited

Answer 1

(a) ABO blood group is controlled by I gene. I genes has 3 alleles: $I^A$, $I^B$, i.

Thus, ABO blood group is a good example of multiple allelism.

(b) $I^A{I}^A$ (mother) x $I^B{I}^B$ (father)

Progeny: $I^A{I}^B$
So, the blood group of the progeny will have the blood group Ab.
This shows co-dominance pattern of inheritance.