Kodominance

Kodominance (more commonly spelled codominance) is a pattern of genetic inheritance in which two different alleles of a gene are both fully expressed in a heterozygote, producing a phenotype that shows distinct contributions from each allele rather than blending them. In codominance neither allele is recessive; both phenotypic effects are visible simultaneously.

A classic example is the human ABO blood group system: the IA and IB alleles are codominant, so an individual who inherits both expresses the AB blood type, displaying antigenic properties of both alleles. Other examples include certain coat-color phenotypes in animals, such as roan coloration in cattle, where hairs of both colors appear. At the molecular level codominance typically arises when different alleles produce stable but different gene products (proteins or structures) that coexist in the organism.

Codominance differs from incomplete dominance, in which heterozygotes show an intermediate or blended phenotype; in codominance the parental phenotypes are simultaneously evident. In simple Mendelian crosses involving codominant alleles, heterozygote by heterozygote matings yield a 1:2:1 ratio of the two homozygotes and the codominant heterozygote phenotype.

Understanding codominance is important for genetics, medicine, and breeding, as it affects phenotype prediction, blood transfusion compatibility, and the interpretation of inheritance patterns. The term is widely used in genetics literature, with "codominance" being the standard spelling in English-language sources.