Which pattern describes a situation where the phenotypes produced by both alleles are clearly expressed in the heterozygote?

Which pattern describes a situation where the phenotypes produced by both alleles are clearly expressed in the heterozygote?

• A. Incomplete dominance
• B. Codominance
• C. Polygenic inheritance
• D. Environmental influence

Answer: (B)

Codominance is when the heterozygous genotype expresses both alleles’ traits distinctly, so you can see two phenotypes at once and neither allele masks the other. This happens because neither allele is dominant or recessive, allowing both to contribute to the phenotype. A classic example is the AB blood type, where A and B antigens are both present on red blood cells. Another example is roan coat color in cattle, where red and white hairs appear together rather than mixing into a single intermediate color. This differs from incomplete dominance, where the heterozygote shows an intermediate blend (like pink from red and white). It also isn’t about many genes (polygenic inheritance) or environmental effects, which alter trait expression without two clearly expressed alleles.

Codominance is when the heterozygous genotype expresses both alleles’ traits distinctly, so you can see two phenotypes at once and neither allele masks the other. This happens because neither allele is dominant or recessive, allowing both to contribute to the phenotype. A classic example is the AB blood type, where A and B antigens are both present on red blood cells. Another example is roan coat color in cattle, where red and white hairs appear together rather than mixing into a single intermediate color. This differs from incomplete dominance, where the heterozygote shows an intermediate blend (like pink from red and white). It also isn’t about many genes (polygenic inheritance) or environmental effects, which alter trait expression without two clearly expressed alleles.