Continuous variation in traits suggests what about the genetic contributions?

Continuous variation in traits indicates that the traits are the result of the combined effects of two or more genes, which contribute to the phenotype in an additive manner. This means that rather than being determined solely by one gene, many different genes (often termed polygenic traits) interact to produce a range of phenotypic expressions.

For example, traits such as height, skin color, and weight are classic examples of continuous variation. Each contributing gene adds a small amount to the overall phenotype, leading to a spectrum rather than distinct categories. This additive genetic effect leads to a bell-shaped curve when the distribution of the trait is graphed, thereby illustrating the continuous nature of the variation.

This understanding sets continuous traits apart from traits governed by a single gene, which typically show discrete phenotypic categories rather than a gradient.