The problem is addressed by simulating the effects of two candidate loci and environment on liability to a psychiatric disorder. A general biometrical-genetic model for the additive, dominance and epistatic effects of the two loci (c.f. Mather and Jinks 1982) characterizes the main effects of the genes on liability and the (linear) response of genotypes to a continuously variable environmental covariate (G × E interaction). The model has been widely used in experimental organisms, including plants and fruitflies and has the advantage of capturing classical patterns of non-allelic interaction (epistasis) as special cases of the general model.
