# Why are alleles IA and IB considered codominant?

Mar 20, 2018

Alleles $I A$ and $I B$ are considered codominant as both these alleles dominate over recessive allele. $i$ .

#### Explanation:

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

However, when both these dominant alleles $I A$ and $I B$ are present together, none of these is able to interfere with the expression of other allele. Thus, the genoptype $I A I B$ 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: $I A I A , I A i$
Blood group B : $I B I B , I B i$
Blood group AB: $I A I B$
Blood group O: $i i$