4poligen

4poligen is a simplified, hypothetical model in quantitative genetics used to illustrate polygenic inheritance with four independent genetic loci. It is not a standard term in the scientific literature but is sometimes used in textbooks or simulations to teach additive effects across a small number of genes.

Model framework: The trait is assumed to be influenced by four loci, each contributing additively to the phenotype. If each locus has two alleles and additive effect sizes are α1...α4, the genetic component is G = α1x1 + α2x2 + α3x3 + α4x4, where xi is the dosage of the effect allele (0, 1, or 2). The phenotype P = μ + G + E, with E representing environmental effects. Under random mating and independence, the phenotypic distribution approximates normal due to the central limit theorem, especially as more loci are included.

Uses and interpretation: 4poligen is often used to demonstrate how additive genetic variance contributes to trait variation, how allele frequencies shape the mean and variance, and how environmental variance interacts with genetics. It is useful for homework problems, simulations, and introductory discussions of quantitative genetics.

Limitations: Real traits involve many more loci and often non-additive effects such as dominance and epistasis; gene interactions and linkage can alter variance; environmental factors can interact with genotype; five or more loci would better approximate polygenic traits; thus 4poligen should be treated as a teaching abstraction rather than a realistic model.

See also: polygenic trait, quantitative genetics.