Codominance

Definition

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.

5 Must Know Facts For Your Next Test

1. In codominance, neither allele is recessive or masked by the other.
2. Human blood type AB is an example of codominance, where both A and B antigens are equally expressed.
3. Codominance can be observed in plants like roan cattle, which have both red and white hairs.
4. The phenotypic ratio for a codominant cross between two heterozygotes (e.g., RW x RW) typically results in a 1:2:1 ratio.
5. Codominance differs from incomplete dominance, where the heterozygous phenotype is an intermediate blend of the two alleles.

Review Questions

• What is an example of codominance in humans?
• How does codominance differ from incomplete dominance?
• What would be the phenotypic ratio in a cross showing codominance between two heterozygous individuals?

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.

homozygous: Having two identical alleles for a specific gene.