Codominance
Say it: koh-DOM-ih-nuns
Codominance is a pattern of inheritance in which both alleles in a heterozygote are fully expressed, so the traits of both appear together.
Also: co-dominance, codominant inheritance
Definition
What is codominance?
Codominance is a relationship between two alleles of the same gene in which a heterozygote, an individual with one copy of each, expresses both of them at full strength. Neither allele masks the other, and the result is not a blend: the product of each allele can be detected separately in the same individual.
The best-known example is the human ABO blood group. The A and B alleles encode slightly different versions of an enzyme that attaches a sugar to molecules on red blood cell surfaces, each version adding a different sugar. A person who inherits A from one parent and B from the other therefore carries both A and B antigens and has blood type AB. The MN blood group works in the same way, and roan cattle have a coat in which fully red and fully white hairs grow side by side. Because each genotype gives its own phenotype, a cross between two heterozygotes yields three recognizable kinds of offspring in a 1:2:1 ratio.
Codominance is often contrasted with incomplete dominance, in which the heterozygote looks intermediate. Several relationships can exist within one gene: in the ABO system, A and B are codominant with each other, but both are dominant over O.
Word parts
Where does the word “codominance” come from?
- co-
- together, withLatin co-, com-
- domin-
- to rule, to masterLatin dominari
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Terms that go with it
- Incomplete dominanceIncomplete dominance is a pattern of inheritance in which a heterozygote has a phenotype intermediate between those of the two homozygotes.
- AlleleAn allele is any of the alternative forms of a gene or DNA sequence that can occupy the same position, or locus, on a chromosome.
- HeterozygousHeterozygous describes an organism that carries two different alleles of a gene at a given locus, such as one dominant and one recessive allele.
- AntigenAn antigen is any molecule the immune system can recognize as a target, especially one that prompts antibodies or T cells to respond against it.
- Red blood cellA red blood cell, or erythrocyte, is a disc-shaped blood cell without a nucleus that is packed with hemoglobin and carries oxygen around the body.
- Dominant alleleA dominant allele is a version of a gene whose effect shows in the phenotype even when only one copy is present, masking a recessive allele.
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Checked against
Written for biofideX in plain words, after checking these references:
- NHGRI Talking Glossary: Codominance
- OpenStax Biology 2e, 12.2 Characteristics and Traits
- MedlinePlus Genetics: What are the different ways a genetic condition can be inherited?
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