What is codominance?

What is codominance?

• A. Only one allele is expressed.
• B. Dominant allele completely masks the recessive.
• C. Both alleles are fully and simultaneously expressed in the phenotype.
• D. The trait is influenced by the environment.

Answer: (C)

Codominance is when two different alleles at a gene locus are both expressed in the phenotype at the same time, so you see both traits rather than one masking the other. A classic example is the AB blood type, where A and B antigens are both present on red blood cells because the IA and IB alleles are codominant. Another example is roan coat color in cattle, where red and white hairs are both expressed. This differs from complete dominance, where one allele completely masks the other, and from environmental effects, where the environment influences the trait rather than showing both alleles' products. Therefore, the phenotype reflects both alleles being active.

Codominance is when two different alleles at a gene locus are both expressed in the phenotype at the same time, so you see both traits rather than one masking the other. A classic example is the AB blood type, where A and B antigens are both present on red blood cells because the IA and IB alleles are codominant. Another example is roan coat color in cattle, where red and white hairs are both expressed. This differs from complete dominance, where one allele completely masks the other, and from environmental effects, where the environment influences the trait rather than showing both alleles' products. Therefore, the phenotype reflects both alleles being active.