A graphical depiction of the correlation matrix for gene pairs where both genes belong to the functional category of interest (A) and the correlation matrix for gene pairs where one gene belongs to the functional category of interest and the other one to the background (B). Note that elements on the main diagonal of A are equal to one, and that A is symmetric (as indicated by the dashed line). t-tests in our algorithm are calculated between the sets of correlations in A and B (for A we use the upper triangular part only).