Hierarchical cluster analysis of 937 samples. Analysis of 937 samples (columns) using a set of 1019 differentially expressed genes (rows). The normalized expression value for each gene is coded by color (SD from mean). Red cells indicate high expression, and green cells indicate low expression. Bars separate the major leukemia types. For each of the 13 classes, the top 100 differentially expressed genes, according to t test statistic, were used. Of the 1300 genes, 281 were repeatedly identified as important diagnostic markers and overlapped among the lists of the top 100 genes, resulting in 1019 nonoverlapping genes.