Hierarchical clustering analysis of four experimental groups of MNU-treated mice. Expression data from 303 qualified probes (left). The four experimental groups were classified into two clusters (Groups A/C) and (Groups B/D) based on similarities in expression patterns. Each row represents a probe and each column represents a experimental group (Groups A-D). As shown in the color bar, green indicates up-regulation; red indicates down-regulation; and black indicates no change. Thirty-one probes constituted a cluster of probes up-regulated only in Group D (right).