kódominance

Codominance is a type of genetic inheritance where both alleles for a trait in a heterozygous individual are fully expressed. Unlike incomplete dominance, where the heterozygous phenotype is an intermediate blend of the two homozygous phenotypes, codominance results in both alleles contributing distinctly to the observable trait. This means that an individual with codominant alleles will exhibit characteristics of both alleles simultaneously.

A classic example of codominance is the ABO blood group system in humans. The gene for ABO blood type has three common alleles: I^A, I^B, and i. Individuals with genotype I^A I^A or I^A i have blood type A, while those with I^B I^B or I^B i have blood type B. Individuals with genotype ii have blood type O. However, when both the I^A and I^B alleles are present (genotype I^A I^B), the resulting phenotype is blood type AB. In this case, both the A antigen and the B antigen are present on the surface of red blood cells, demonstrating the full expression of both alleles.

Another example is found in certain breeds of cattle and horses. For instance, the roan coat color in shorthorn cattle is a result of codominance. Red shorthorns are homozygous for the red allele, and white shorthorns are homozygous for the white allele. Roan shorthorns are heterozygous and display a mixture of both red and white hairs, not a blended reddish-brown color. These distinct expressions of both alleles are the hallmark of codominance.