Which statement best describes incomplete dominance?

Which statement best describes incomplete dominance?

• A. One allele is not completely dominant over another allele
• B. Both alleles are equally dominant and produce a blended phenotype
• C. The dominant allele completely masks the recessive allele in heterozygotes
• D. The environment determines the phenotype

Answer: (A)

Incomplete dominance happens when neither allele is completely dominant over the other, so a heterozygote shows a phenotype that is intermediate between the two homozygotes. This means each allele contributes to the trait, yielding a blend rather than one allele completely masking the other. For example, crossing red and white flowers can produce pink offspring, with the pink color reflecting contributions from both red and white alleles. That’s why the best description is that one allele is not completely dominant over the other. If the environment determined the trait, or if a dominant allele completely masked the recessive one, those would describe environmental effects or complete dominance, not incomplete dominance. Saying both alleles are equally dominant and produce a blended phenotype isn’t the standard way to capture the idea, since dominance describes how one allele interacts with another, and incomplete dominance specifically means neither allele is fully dominant.

Incomplete dominance happens when neither allele is completely dominant over the other, so a heterozygote shows a phenotype that is intermediate between the two homozygotes. This means each allele contributes to the trait, yielding a blend rather than one allele completely masking the other. For example, crossing red and white flowers can produce pink offspring, with the pink color reflecting contributions from both red and white alleles.

That’s why the best description is that one allele is not completely dominant over the other. If the environment determined the trait, or if a dominant allele completely masked the recessive one, those would describe environmental effects or complete dominance, not incomplete dominance. Saying both alleles are equally dominant and produce a blended phenotype isn’t the standard way to capture the idea, since dominance describes how one allele interacts with another, and incomplete dominance specifically means neither allele is fully dominant.