Question

Why are alleles $I^A$ and $I^B$ considered codominant?

Answer 1

Many of the rules of current genetics and inheritance were developed by Gregor Mendel, a geneticist. He discovered that an offspring will inherit one allele (gene product) from each of its parents through research with pea plants. The organism and the type of dominance expressed determine how these alleles are displayed.

Complete answer:
$I^A$ and $I^B$ are codominant, but Io has the upper hand. When a person receives both an $I^A$ and an $I^B$ allele, their blood type is type AB, which expresses both A and B antigen features.

Alleles $I^A$ and $I^B$ are regarded as codominant since they both outnumber recessive alleles.

Antigen A and B are produced by alleles $I^A$ and $I^B$, respectively. Antigen is not produced by the recessive allele i. Alleles $I^A$ and $I^B$ will dominate over allele I and yield antigens A and B, respectively, if they are present alongside recessive allele i.

When both dominant alleles $I^A$ and $I^B$ are present, however, neither of them can interfere with the expression of the other allele. As a result, the $I^A$ $I^B$ genotype will produce both antigens A and B.

presence of antigen on R.B.C. determines an individual's blood group.
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: ii.

The phenotype of heterozygote, which expresses the traits of both alleles, can be used to detect codominance.

Note:
A link between two variants of a gene is known as codominance. Each parent gives each child one allele, which is a variant of a gene. If the alleles are different, the dominant allele will normally be manifested, while the recessive allele's effect will be muted. However, in codominance, neither allele is recessive, and both phenotypes are expressed.