What is the definition of incomplete dominance?

Incomplete dominance is a genetic phenomenon where the phenotype of a heterozygote is intermediate between the phenotypes of the two homozygotes. This occurs when one allele does not completely mask the effect of the other allele, resulting in a blending effect. For instance, if one parent contributes a red-flower gene and the other contributes a white-flower gene, the offspring may display pink flowers, illustrating the blending of traits due to the influence of both alleles, even though neither is fully dominant.

The other options do not accurately describe incomplete dominance. The first option refers to codominance, where both alleles in a heterozygous condition are fully expressed, resulting in a distinct phenotype for each allele. The third option describes a scenario where both alleles are dominant, typically indicating codominance rather than incomplete dominance. The last option suggests that no phenotype is expressed, which does not reflect the nature of incomplete dominance, as phenotypes do result from the interaction of the alleles, albeit in a blended form.