Question

How does the gene 'I' control ABO blood groups in humans ? Write the effect the gene has on the structure of red blood cells.

Answer 1

In humans, the ABO blood groups are controlled by a gene called gene ‘I’. It has three alleles, namely I^A, I^B and i. A person possesses any two of the three alleles. I^A and I ^B dominate over i. But with each other, I^A and I^B are co-dominant.

Table Showing the Genetic Basis of Blood Groups in Human Population is given as follows

 

Allele from Parent 1	Allele from Parent 2	Genotype of offspring	Blood type of offspring
I A	I A	I A I A	A
I A	I B	I A I B	AB
I A	i	I A i	A
I B	I A	I A I B	AB
I B	I B	I B I B	B
I B	i	I B i	B
i	i	i i	O

These alleles helps to determine the blood group of a person.

The plasma membrane of red blood cells has sugar polymers that protrude out from its surface and the kind of sugar is regulated by the gene 'I' of ABO blood group. The alleles  I^A and I^B produce A and B types of sugar, while allele i does not produce any sugar.