a-b. Clustered image maps showing patterns of expression relationship among genes, platforms, and cell lines. The axes were ordered by hierarchical clustering using an uncentered correlation and the average linkage algorithm for 909 genes expressed at a two-fold or greater level in at least two of the six cell lines. (a) Clustering of all 909 genes (b) A subcluster of 41 genes to show correct clustering and congruence of expression values. As indicated by the cluster trees, all three platforms gave essentially the same relationships among the six cell lines.