Which statement correctly differentiates codominance from incomplete dominance?

Which statement correctly differentiates codominance from incomplete dominance?

• A. Codominance shows both alleles in phenotype.
• B. Codominance yields an intermediate phenotype.
• C. Incomplete dominance shows both alleles in phenotype.
• D. They are the same phenomenon.

Answer: (A)

The key idea is how alleles appear in the organism’s traits. In codominance, both alleles are expressed fully and separately, so you can observe both traits in the phenotype. A classic example is the AB blood type, where A and B antigens are both present on the surface of red blood cells, with neither allele dominating the other. In contrast, incomplete dominance produces an intermediate phenotype, a blend between the two alleles—like red and white flowers producing pink offspring—where neither allele is fully expressed on its own. So the statement that codominance shows both alleles in the phenotype correctly distinguishes it from incomplete dominance. The other options describe an intermediate phenotype for codominance, or equate the two phenomena, which isn’t accurate.

The key idea is how alleles appear in the organism’s traits. In codominance, both alleles are expressed fully and separately, so you can observe both traits in the phenotype. A classic example is the AB blood type, where A and B antigens are both present on the surface of red blood cells, with neither allele dominating the other.

In contrast, incomplete dominance produces an intermediate phenotype, a blend between the two alleles—like red and white flowers producing pink offspring—where neither allele is fully expressed on its own.

So the statement that codominance shows both alleles in the phenotype correctly distinguishes it from incomplete dominance. The other options describe an intermediate phenotype for codominance, or equate the two phenomena, which isn’t accurate.