Advanced Placement (AP) Biology Practice Exam

Which of the following illustrates an example of a polygenic trait?

1. Blood Type

2. Canary color

3. Human height

4. Skin pigmentation in a lab rat

The correct answer is: Human height

A polygenic trait is one that is influenced by multiple genes, resulting in a continuous range of phenotypes rather than distinct categories. Human height is a prime example of a polygenic trait because it is determined by the additive effects of several genes as well as environmental factors. This means that rather than being classified into a few specific categories, such as tall or short, human height can exhibit a wide range of measurements that reflect the cumulative contribution of many different alleles. This complexity results in a bell curve distribution of heights within a population, showcasing the variations that can arise from the interaction of multiple genes. It highlights how traits can be influenced by many factors, leading to diverse phenotypic expressions. In contrast, blood type is determined by a single gene with distinct categories, and while canary color and skin pigmentation in lab rats have genetic components, they may not exhibit the same level of polygenic inheritance or may involve additional genetic factors that influence expression in a manner that does not reflect a simple polygenic trait model.