Polygenic traits are those traits that are controlled by more than one gene. Such traits may even be controlled by genes located on entirely different chromosomes. Human height, eye and hair color are examples of polygenic traits. Skin color is another polygenic trait for humans and a variety of other animals.
Other polygenic traits in animals include weaning weight, weight, hair color and length. Behavioral characteristics of animals are often controlled by multiple gene loci as well, although the environment, in the form of parental care, often influences behavior as well.
Polygenic traits often result in bell curve-like distributions of traits within populations. For example, if the height of a population of people is plotted on a graph, it reveals a bell-shaped curve because very few of the people in the population are very short or very tall. Instead, most people fall somewhere in the middle.
Most polygenic traits are at least partially affected by the environment. For instance, human height is largely based on a person's genetic code, but a human’s diet, health and hormones are also responsible for determining their height. These environmental factors are responsible for about 10 percent of a person’s height, while the genetic factors are responsible for the remaining 90 percent.