Fig. 1. A. Example of the meta-gene MEG273. An arrow points from gene X to gene Y if the protein sequence of Y had the best BLAST score to Xs protein sequence among all protein sequences in Ys database. B. Compendiums of microarray expression data from four organisms included in the analysis. Color shows type of DNA microarray experiment. C. Network construction and visualization procedure. Thick, thin and gray arrows indicate strong, medium and weak correlations, respectively. A P-value was computed between two meta-genes based on the Pearson correlations of their respective genes. Since the P-value for MEG1 and MEG2 is below the cutoff of 0.05, these two meta-genes are linked in the multiple species co-expression network. The P-values were used to cluster meta-genes together on a terrain map using VxInsight (15). Distance in the X-Y plane indicates degree of conserved co-expression, and altitude indicates local density of genes. Shown is the X-Y scatter plot and three-dimensional representation for 3416 meta-genes.