Incomplete dominance occurs when

A. both alleles are expressed equally in the phenotype.

B. both alleles are completely dominant.

C. both alleles are completely recessive.

D. the dominant allele is not entirely dominant.

The answer to this is a because it occurs when the phenotype of the heterozygous genotype is distinct from and often intermediate to the phenotypes of the homozygous genotypes. For example, the snapdragon flower color is homozygous for either red or white.