Question

What do you mean by codominance? Explain it with examples of blood groups in human beings.

Answer 1

Hint: Codominance is a condition in which no allele can mask the other allele, where the expression of both alleles can be seen, and it is said to be a heterozygous condition, one of a good example for the Codominance is ABO blood group system of humans

Complete answer:
- Codominance is a condition in which offspring show both parents similarity, and it is due to the blending of alleles
- As above said ABO blood group system of humans is the best example for the Codominance.
- There are mainly four blood groups in humans, irrespective of the Rh factor such as A, B, AB, O.
- These blood groups are named based on the antigen present on the surface of the red blood cell.
- For example, if a person has a blood group A, which means his RBC surface contains antigen A, where this all is determined by the gene I.
- Mainly this gene I is again divided into 3 types, IA, IB, and i, here both IA and IB produce antigens but i do not produce any antigen, so IA and IB are dominant over the allele i
- As we all know that diploid organisms mainly contain 2 types of alleles, based on the combination of alleles present on the gene, the blood group of the individual is expressed.

So the list of genotype and blood groups are as follows
IA, IA --- A blood group
IB, IB--- B blood group
IA, IB--- AB blood group
IA, i---- A blood group
IB, i---- B blood group
i,i----- O blood group

- We know that IA, IB are dominant alleles, whereas i is the recessive allele, from the above-given list alleles IA,i express the blood group A as IA is dominant and possess A antigen, where i is recessive and does not have any antigen.
- At the same time IA, IB expresses the AB blood group, where both alleles are dominant and express both of the antigens which are the perfect example of Codominance.

Note: The generation, where the offspring produce the genetic characteristics of both the parents and at the same time, the phenotypic expression, is said to be Codominance, there is another term called incomplete dominance, where the dominance is not in a complete manner which results in intermediate progeny.