Kodominant

Codominance is a pattern of inheritance in which both alleles of a gene in a heterozygous organism are fully expressed, producing a phenotype that displays both forms of the trait. This differs from complete dominance, where one allele masks the other, and from incomplete dominance, where the phenotype is a blend of the two alleles.

In codominant systems, neither allele is recessive. Instead, each allele contributes to the phenotype in a way that can be observed distinctly. This often involves the presence of two different functional products or antigens that are simultaneously detectable in the organism.

Classic examples illustrate codominance in humans and other organisms. In the ABO blood group system, the IA and IB alleles are codominant; individuals with IAIB express both A and B antigens on red blood cells, producing the AB blood type, while IAIO and IBIO individuals express only A or B, respectively, and IOIO individuals express neither antigen. The MN blood group is another example, where M and N alleles are codominant, resulting in individuals with M, N, or MN antigens on red cells depending on their genotype. A well-known molecular example is the sickle cell trait, where individuals with HbA HbS produce both normal and abnormal hemoglobin, illustrating codominant expression at the protein level.

Codominance is a form of Mendelian inheritance in which heterozygotes show a distinct phenotype influenced by both alleles. It is important for interpreting genetic tests, breeding results, and the expression of certain traits in medical and agricultural contexts.