additivevariantti

Additivevariantti is a term used in quantitative genetics to describe a genetic variant whose effect on a trait adds linearly to the effects of other variants. Additivity means the contribution of each allele sums across loci, without interaction effects such as dominance or epistasis.

Etymology: The word combines English “additive” with Finnish “variantti,” and is used in Finnish-language genetics literature to discuss additive components of genetic variation.

Definition and framework: An additive variantti is a genetic variant whose impact on a trait is modeled as additive. The cumulative effect of many additive variants contributes to the additive genetic variance Va, a component of heritability.

Identification: In practice, additive effects are estimated with linear models in genome-wide association studies (GWAS) using allele dosages that assume additivity. The resulting effect sizes are interpreted as the average change in the trait per copy of the effect allele.

Applications and significance: Additive effects underpin selection in breeding and the prediction of trait values through polygenic scores. Understanding additive variantti helps partition genetic influence from environmental factors.

Limitations: Many traits involve non-additive interactions between loci (dominance and epistasis). The additive model is an approximation that may explain only part of the genetic variance.

Example: For a SNP with two alleles, each copy of the effect allele increases height by an average 0.3 cm; two copies give about 0.6 cm more height due to this variant.

See also: additive genetic variance, polygenic trait, GWAS.