13. The method of claim 1 wherein said step of computing mutual information generates an adjacency matrix or a computationally equivalent representation of mutual information values describing pairwise expression relationships between species represented in said compendium, said matrix having rows and columns of mutual information values, wherein the value in each cell in said matrix is the mutual information between two genes' expression profiles.
14. The method of claim 13 wherein said step of applying a background correction comprises the steps of estimating a likelihood of the mutual information score, MI, for a given pair of genes, genes i and j, representing row or column i and row or column j of said adjacency matrix, by comparing the mutual information score, MI ij , for that pair to a background distribution of mutual information values.