Algonquin College Health Program Assessment (AC-HPAT) Practice Exam

What is demonstrated when a red snapdragon is crossed with a white one and all F1 hybrids have pink flowers?

1. Complete dominance

2. Co-dominance

3. Incomplete dominance

4. Polygenic inheritance

The correct answer is: Incomplete dominance

When a red snapdragon is crossed with a white snapdragon, resulting in all F1 hybrids having pink flowers, the phenomenon being demonstrated is known as incomplete dominance. In this genetic scenario, neither the red nor the white trait is completely dominant over the other, leading to a blending of traits in the offspring. Incomplete dominance occurs when the heterozygous phenotype (the pink flowers in this case) is intermediate between the phenotypes of the two homozygous parents (red and white flowers). Instead of expressing the traits fully, the alleles blend to form a third distinct trait. This is clearly illustrated through the pink flower color, which is neither fully red nor fully white but rather a combination of both. The other concepts mentioned do not accurately describe this genetic interaction. Complete dominance refers to a situation where one allele completely masks the other, resulting in a phenotype that resembles one parent only. Co-dominance involves both alleles being expressed simultaneously and distinctly in the phenotype, such as in AB blood type, where both A and B antigens are present. Polygenic inheritance describes a situation where multiple genes govern a trait, leading to a continuous range of phenotypes, such as height in humans, rather than a simple blending of two traits.