Editing Quantitative genetics (section)

=== Environmental variance ===
The environmental variance is phenotypic variability, which cannot be ascribed to genetics. This sounds simple, but the experimental design needed to separate the two needs very careful planning. Even the "external" environment can be divided into spatial and temporal components ("Sites" and "Years"); or into partitions such as "litter" or "family", and "culture" or "history". These components are very dependent upon the actual experimental model used to do the research. Such issues are very important when doing the research itself, but in this article on quantitative genetics this overview may suffice.

It is an appropriate place, however, for a summary:

Phenotypic variance = genotypic variances + environmental variances + [[genotype-environment interaction]] + experimental "error" variance

i.e.,  σ<sup>2</sup><sub>P</sub> = σ<sup>2</sup><sub>G</sub> + σ<sup>2</sup><sub>E</sub> + σ<sup>2</sup><sub>GE</sub> + σ<sup>2</sup>

'' or'' 
σ<sup>2</sup><sub>P</sub> = σ<sup>2</sup><sub>A</sub> + σ<sup>2</sup><sub>D</sub> + σ<sup>2</sup><sub>I</sub> + σ<sup>2</sup><sub>E</sub> + σ<sup>2</sup><sub>GE</sub> +  σ<sup>2</sup>

after partitioning the genotypic variance (G) into component variances "genic" (A), "quasi-dominance" (D), and "epistatic" (I).<ref>It is common practice ''not'' to have a subscript on the experimental "error" variance.</ref>

The environmental variance will appear in other sections, such as "Heritability" and "Correlated attributes".