Codominance is a form of inheritance where both alleles in a gene pair are fully expressed in the heterozygous condition. This results in offspring with a phenotype that shows both traits simultaneously without blending.
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In codominance, neither allele is recessive or masked by the other.
Human blood type AB is an example of codominance, where both A and B antigens are equally expressed.
Codominance can be observed in plants like roan cattle, which have both red and white hairs.
The phenotypic ratio for a codominant cross between two heterozygotes (e.g., RW x RW) typically results in a 1:2:1 ratio.
Codominance differs from incomplete dominance, where the heterozygous phenotype is an intermediate blend of the two alleles.
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Related terms
allele: A variant form of a gene at a particular locus on a chromosome.
incomplete_dominance: A form of inheritance where the heterozygous phenotype is intermediate between the two homozygous phenotypes.