Fig. 1.

Schematic representation of the basic models underlying the polygenic methods reviewed. All models assume that a phenotype (P) is influenced by genetic (G) and environmental (E) factors (with environmental defined loosely as anything not captured by G including stochastic variation and measurement error). (a) Model which considers only one phenotype and no gene expression. (b) Model which considers only one phenotype and gene expression (X). (c) Model which considers two or more phenotypes and no gene expression. Methods can be grouped into those where the focus lies on individual SNPs, genes or people (nodes highlighted), and those where the focus lies on aggregate measures affecting the relationship between genetic and environmental factors and a phenotype (edges highlighted).