Humber Admissions Practice Test

What is a defining feature of incomplete dominance?

1. The phenotypes of both homozygous traits are expressed fully

2. The heterozygous phenotype is a blend of the two homozygous phenotypes

3. Only one allele is expressed in the phenotype

4. Traits are influenced by dominant alleles only

The correct answer is: The heterozygous phenotype is a blend of the two homozygous phenotypes

A defining feature of incomplete dominance is that the heterozygous phenotype results in a blend of the two homozygous phenotypes. In this form of inheritance, neither allele is fully dominant over the other, leading to an intermediate expression of traits. For example, if one parent contributes a red flower trait and another parent contributes a white flower trait, the offspring may display pink flowers, which visually represents this blending effect. The other options do not accurately describe incomplete dominance. Some suggest that both homozygous traits are expressed fully, which would be more characteristic of codominance rather than incomplete dominance. Another option states that only one allele is expressed, which aligns more with complete dominance, where the dominant allele masks the expression of the recessive allele. Lastly, the idea that traits are influenced by dominant alleles only also does not reflect the mechanism of incomplete dominance, where both alleles influence the phenotype, though not to the full extent as would occur in complete dominance.