A cluster of approximately 50 genes that is observed, using Affymetrix GeneChips, to have greater mRNA expression in adenocarcinoma of the colon than in normal colon tissue. The genes are distributed along the vertical axis, and the tissue samples along the horizontal axis. This cluster is extracted from a larger data table that had been reorganized by a two-way clustering algorithm to discern subtle, distributed patterns of gene expression. Each color patch represents the expression level of the associated gene in that tissue sample, with a continuum of expression levels from dark green (lowest) to bright red (highest). For details, see the article by Notterman et al. in this issue.