Which of the following is an example of incomplete dominance?

Which of the following is an example of incomplete dominance?

• A. Red and white snapdragon flowers producing pink flowers
• B. ABO blood types in humans
• C. Full black coat color in Labrador Retrievers
• D. Blue eyes from a heterozygous genotype

Answer: (A)

Incomplete dominance occurs when the phenotype of the heterozygote is a blend of the two homozygous phenotypes. In the case of red and white snapdragon flowers producing pink flowers, the red flower (which can be thought of as one homozygous genotype) and the white flower (the other homozygous genotype) combine to produce a new phenotype in the heterozygous condition—pink flowers. This blending illustrates how neither allele is completely dominant over the other, resulting in a distinct intermediate phenotype. The other choices do not illustrate incomplete dominance. ABO blood types represent co-dominance where both A and B alleles are fully expressed in the presence of the other. Full black coat color in Labrador Retrievers indicates complete dominance, where the black coat allele completely masks any other coat color alleles. The example of blue eyes from a heterozygous genotype does not demonstrate incomplete dominance, as it typically indicates a situation where one allele is simply dominant over another, resulting in a single visible phenotype without blending.

Incomplete dominance occurs when the phenotype of the heterozygote is a blend of the two homozygous phenotypes. In the case of red and white snapdragon flowers producing pink flowers, the red flower (which can be thought of as one homozygous genotype) and the white flower (the other homozygous genotype) combine to produce a new phenotype in the heterozygous condition—pink flowers. This blending illustrates how neither allele is completely dominant over the other, resulting in a distinct intermediate phenotype.

The other choices do not illustrate incomplete dominance. ABO blood types represent co-dominance where both A and B alleles are fully expressed in the presence of the other. Full black coat color in Labrador Retrievers indicates complete dominance, where the black coat allele completely masks any other coat color alleles. The example of blue eyes from a heterozygous genotype does not demonstrate incomplete dominance, as it typically indicates a situation where one allele is simply dominant over another, resulting in a single visible phenotype without blending.