(a) Why is human ABO blood group gene considered a good example of multiple alleles?

(b) Work out a cross up to F1 generation only, between a mother with blood group A (Homozygous) and the father with blood group B (Homozygous). Explain the pattern of inheritance exhibited.

(a) The gene I controlled the ABO blood groups. A gene is represented by two alleles. The plasma membrane of the red blood cells surface has sugar polymers and the type of sugar is controlled by the gene. The gene (I) has three alleles IA, I B and i. Thus, it is an example of multiple alleles. IA and IB are completely dominant over i, (because i does not produce any sugar). These alleles decide the blood group of person.

(b) As given, a mother with blood group A (Homozygous) and the father with blood group B (Homozygous).

Therefore, the child will have blood group AB.

The pattern of inheritance is called co-dominance.