Poligénes

Poligénes are genes that contribute to phenotypic variation in a trait through small additive effects at many loci. A polygenic trait is influenced by multiple genes, each with a small effect, rather than by a single gene of large effect. The combined action results in continuous variation across individuals, often approximating a normal distribution. Common examples include human height, skin coloration, and many metabolic traits; environmental factors also shape final phenotype.

Inheritance is polygenic: Because each gene's effect is small, Mendelian ratios do not apply; rather, the trait follows polygenic inheritance. Additive effects accumulate; non-additive effects like dominance and epistasis can occur but are less predictable.

Historical context: The concept emerged in the early 20th century to reconcile Mendelian genetics with continuous trait variation. Ronald A. Fisher formalized the theory of polygenic inheritance in 1918, laying the foundation for quantitative genetics.

Modern relevance: Genome-wide association studies have identified thousands of loci with small effects that together influence complex traits. Polygenic risk scores aggregate these effects to estimate genetic predisposition to diseases or traits. However, much heritability remains "missing" due to rare variants, gene-environment interactions, and statistical limitations.

Distinctions: Polygenes are contrasted with major genes responsible for monogenic traits. Polygenic models explain why traits vary continuously rather than discretely.