In genetics, denoting an equal degree of dominance of two genes, both being expressed in the phenotype of the individual; e.g., genes A and B of the ABO blood group are c.; individuals with both are type AB.
* * *
co·dom·i·nant (')kō-'däm-ə-nənt adj being fully expressed in the heterozygous condition <the alleles controlling blood groups A and B are \codominant since an individual with both alleles belongs to blood group AB>
codominant n
Medical dictionary. 2011.