Co-dominance is a heterozygous condition in which both alleles of the same gene locus express themselves fully in the phenotype.
It is a condition in which the effect of the recessive gene is not masked by the dominant one, but both are dominant and manifest as phenotypic characteristics.
Co-dominance process:
Because both alleles are expressed, neither phenotype is completely dominant, resulting in a mixed expression.
It makes no difference whether the alleles are dominant or recessive to each other.
If they are capable of producing the protein that can be expressed, codominance will result.
The best example of codominance is the ABO blood group system.
The gene locus is I, and there are three alleles present: A, B, and O.
A and B are recessive for O.
A and B are dominant over one another.
Either of the three being expressed is normal, but when the blood group is discovered to be AB, both A and B are fully expressed.
