Trait heritability describes the share of the genetically determined variability of the trait in its total variability. Individual traits vary in their heritability. The trait heritability of qualitative traits expresses the probability that the traits will be transferred in unaltered form to the next generation while, for quantitative traits, this corresponds to the degree to which they are transferred from one generation to the next. The heritability of a trait is, however, defined in genetics as the fraction of genetically determined variability in the given trait in the total variability of this trait, i.e. also the environmentally determined variability of this trait. Some components of genetically determined variability are inherited from one generation to the next, while others are not. Consequently, attention is concentrated especially on heritability in the narrow sense of the word, i.e. the component of variability of a given trait determined by genes whose effects can be simply added, i.e. genes with additive effect. Other components of heritability include environmentally determined variability, variability determined by interactions between alleles in a single locus (the dominance component) and variability determined by interactions between alleles in various loci (the epistasis component) It is, of course, possible to also define other components of the total variability, with contributions, e.g., from interactions between the environment and dominance, interactions between dominance and epistasis, etc. The evolution of a certain trait through selection is fundamentally affected by the additive genetically determined variability; the other components of the variability mostly reduce the effectiveness of selection. See also Heredity.

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The classical Darwinian theory of evolution can explain the evolution of adaptive traits only in asexual organisms. The frozen plasticity theory is much more general: It can also explain the origin and evolution of adaptive traits in both asexual and sexual organisms Read more