Both alleles are fully expressed in the heterozygote, as in the AB blood type.
Both alleles produce a visible effect. In the ABO system, IA and IB are codominant, giving AB blood with both antigens; i is recessive. Roan cattle show both red and white hairs.
Codominance differs from incomplete dominance because both traits appear distinctly rather than blending.
Both alleles are fully expressed in the heterozygote, as in the AB blood type.
Codominance is one of the 54 topics in Genetics. It is rated Intermediate, so it suits learners who already know the core vocabulary. Related topics in this area include Dominant and Recessive, Homozygous and Heterozygous, Incomplete Dominance.
Sickle cell trait carriers make both normal and sickle haemoglobin.
Work through the Beginner topics in Genetics first, such as Heredity, Gene, Allele, then return to Codominance. Intermediate topics assume the Beginner vocabulary.
The closest topics to Codominance are Dominant and Recessive, Homozygous and Heterozygous, Incomplete Dominance, Pleiotropy. Comparing them side by side is a good way to see how the ideas connect.
Read the summary and the in-depth section, then use the quick check on the interactive lesson for Codominance. To practise the whole of Genetics, use the Genetics quiz.
Codominance: Both alleles are fully expressed in the heterozygote, as in the AB blood type. Dominant and Recessive: A dominant allele shows its effect when present in one copy; a recessive allele only shows when two copies are present. Read both side by side and note what each one explains.
First, read the summary and write the definition in your own words. Second, read the in-depth section and note any example. Third, compare it with Dominant and Recessive and explain the difference aloud. Finally, take the Genetics quiz and come back to this page for any question you miss.
A dominant allele shows its effect when present in one copy; a recessive allele only shows when two copies are present.
🧬 GeneticsHomozygous means two identical alleles for a gene; heterozygous means two different alleles.
🧬 GeneticsThe heterozygote shows an intermediate phenotype, such as pink flowers from red and white parents.
🧬 GeneticsA single gene influences several apparently unrelated traits, as in Marfan syndrome.
🧬 Genetics