Question

"It is sometimes observed that the F₁ progeny shows a phenotype that resembles both the parents." Explain this type of inheritance using the example of A, B, and O blood groups in human.

Answer 1

Codominance is a heterozygous state in which the phenotypic completely expresses both alleles at a gene locus. Codominant alleles are those that exhibit a distinct impact. Both phenotypes in codominance are partially dominant. The blood type AB is the best illustration of codominance.

Red blood cells come in a variety of forms, including A, B, AB, and O with or without the Rh component. The specific blood group in an organism is determined by the antigen on the surface of red blood cells, which changes.

For example, having blood group A indicates that antigen-A is present on the RBC surface. But the gene I decide this. There are three different allele types for the gene I: IA, IB, and i. While allele-i does not create any antigen, alleles IA and IB each produce two distinct antigens. As a result, alleles IA and IB outnumber allele i. Each diploid organism has two pairs of alleles, as is well known.

As a result, there are two forms of alleles in any given combination in humans. Blood type could be identified based on the mix and dominance of an individual's alleles. The list below includes the various allele combinations and the associated blood group types.

Genotype	Blood type
IAIA	A
IAIB	AB
IAi	A
IBIB	B
IBi	B
ii	O