Question

Why are alleles IA and IB considered codominant?

Answer 1

Alleles `IA` and `IB` are considered codominant as both these alleles dominate over recessive allele. `i` .

Explanation:

Alleles `IA` and `IB` produce antigen A and B, respectively. Recessive allele `i` does not produce any antigen . Allele `IA` and allele `IB` present along with recessive allele `i` will dominate over allele `i` and produce antigen A and B, respectively.

However, when both these dominant alleles `IA` and `IB` are present together, none of these is able to interfere with the expression of other allele. Thus, the genoptype `IAIB` will produce both antigens A and B.

The presence of antigen on R.B.C.s determines the blood group of the individual.

There are 4 blood groups: A, B, AB and O. The genotype of differrent blood groups clearly explains the phenomenon of codominance.

Genotypes of 4 blood groups are as follows:

Blood group A: `IAIA, IAi`
Blood group B : `IB IB , IB i`
Blood group AB: `IAIB`
Blood group O: `ii`