3 Simple Genetic Factor Models

The factor analytic approach outlined above can be readily applied to multivariate genetic problems. This was first suggested by Martin and Eaves (1977) for the analysis of twin data (although in their original publication they use matrices of mean squares and cross-products between and within twin pairs). As in the phenotypic example above, a single common factor is proposed to account for correlations among the variables, but now one such factor is hypothesized for each of the components of variation, genetic, shared environmental, and non-shared environmental. Data from genetically related individuals are used to estimate loadings of variables on common genetic and environmental factors, so that variances and covariances may be explained in terms of these factors.