Changes in global expression patterns of chondrocytes induced by glucosamine and IL-1β. A two-way agglomerative hierarchical clustering of samples. The treatment groups are indicated by the legend on the left (also see text; Gln, glucosamine). Only the normalized signal values of genes with a significant (P < 0.0001) treatment effect were included. Each row represents a sample and each column a gene. Color intensities reflect relative signal values, whereby red represents a higher level of gene expression, and green a lower level relative to the mean across all samples for each gene. On the right, hierarchical clustering of the samples is indicated both within and among treatment groups. Longer lines represent greater dissimilarity between samples. For these samples, one of the untreated control samples and two samples from the glucosamine-alone groups were eliminated from the final analysis because they did not satisfy the quality control criteria of the microarray analysis.