Understanding Codominance: Expression of Both Alleles in Heterozygous Organisms

Codominance

A condition in which neither of two alleles of a gene is dominant or recessive.

Codominance is a mechanism of inheritance in which both alleles of a gene are equally expressed in the phenotype of a heterozygous organism. This means that neither allele is dominant over the other, resulting in a distinct phenotype that expresses both traits equally. This is different from incomplete dominance, where the phenotype of a heterozygous individual is an intermediate of the two homozygous states.

An example of codominance is the human blood type AB. In this case, both alleles, A and B, are expressed fully in the phenotype of the individual who inherits them both, resulting in a blood type that has characteristics of both types A and B. Another example is the roan coat color in cattle, which is the result of codominant alleles for both red and white coat color.

It is important to note that in codominance, there is no blending of traits. Rather, each allele expresses its own distinct trait in the phenotype of the heterozygous individual. Additionally, codominance does not occur in all genes, but only in those where both alleles contribute equally to the phenotype.

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