Semiheritability

Semiheritability is a statistical concept used in quantitative genetics and behavioral sciences to describe the proportion of phenotypic variance in a trait that is attributable to additive genetic effects, while accounting for environmental influences. Unlike heritability, which estimates the overall genetic contribution to trait variation, semiheritability specifically focuses on the additive genetic component—meaning the genetic factors that contribute linearly to the phenotype rather than through dominance or epistasis.

The term was introduced to clarify that not all genetic variance is necessarily heritable in the traditional sense, particularly when environmental factors interact with genetic predispositions. Semiheritability is often estimated using methods such as twin or family-based studies, where differences in trait expression among relatives are compared. For instance, if a trait shows higher similarity between monozygotic twins than dizygotic twins, the additive genetic contribution can be quantified, yielding a semiheritability estimate.

This measure is particularly useful in complex traits, where multiple genes and environmental factors interact. Semiheritability helps researchers distinguish between genetic and environmental influences, providing insights into the potential for selective breeding or genetic improvement in organisms, as well as the role of environmental interventions in modifying trait expression. It is also relevant in human genetics, where it aids in understanding the genetic basis of diseases and behavioral traits while acknowledging the impact of non-genetic factors.