In the context of genetics, what does codominance refer to?

Codominance refers to a genetic condition in which both alleles for a particular gene are fully expressed in the phenotype of an organism. This means that neither allele is dominant or recessive; instead, both traits appear simultaneously and distinctly in the individual. A classic example of codominance is seen in the ABO blood group system, where individuals with one allele for type A and one for type B will express both A and B antigens on their red blood cells, resulting in type AB blood.

This phenomenon contrasts with situations where one allele might mask the expression of another, as seen in complete dominance, or where neither allele makes a contribution to the phenotype, as may occur in cases of incomplete dominance or recessiveness. Understanding codominance helps in grasping the complex nature of genetic inheritance patterns and the diversity of traits observed in organisms.