What defines a polygenic trait?

A polygenic trait is defined by its influence from multiple genes, each contributing to the overall phenotype. This means that rather than a single gene determining a trait, a range of genes work in conjunction, resulting in a continuous variation of the trait.

For example, traits such as height, skin color, and weight in humans are polygenic because they are influenced by several different genes, which can each have various alleles that combine in numerous ways. This genetic complexity allows for a wide spectrum of phenotypes rather than discrete categories.

In contrast, traits influenced by a single gene represent Mendelian traits and lead to more categorical outcomes. Environmental factors, while important, do not define a polygenic trait, as purely environmental traits would not have a genetic component. Lastly, a trait with no genetic basis cannot be classified as polygenic since the definition requires the involvement of multiple genes.