Gene clustering (a) 225 filtered genes are clustered based on their expression profiles across 20 samples. Each gene's expression values are standardized to have mean 0 and SD 1 across 20 samples. Dark blue represents low expression level and dark red high expression level. We might be particularly interested in the cluster colored in blue. (b) The clustering tree after a particular resampling. Although the original 'blue' genes are scattered to various places, we can still determine where the original cluster is, using the criteria described in the text. (c) After resampling 30 times, the reliability of the genes belonging to the original cluster is indicated by the vertical gray-scale bar on the left of the blue-red picture.