Unsupervised Classification and Detection of Co-expressed Genes. (A) Double-Hierarchical clustering of gene expression values (heatmap), in rows by genes, and in columns by samples. Similar samples (columns) generate clusters easily identified. For example, the gene expression of samples A and C is similar across genes. However A and C are different from the rest. Co-expressed genes (rows) form tight and small clusters. A selected cluster framed by dotted lines is shown in B. (B) Hierarchical generation of clusters from a selected group of genes in A.