Hierarchical clustering of the 114 genes that were found to be significantly differentially expressed in at least one comparison between a mutant and the wild-type parent strain. A18, A36, and A48 refer to comparison of whiA mutant cDNA to wild-type cDNA prepared from developmental time points 18 h, 36 h, and 48 h, respectively. H refers to similar comparisons of whiH to wild-type at the given time points, and wt36 and wt48 refer to comparison of cDNA from wild-type strain at 36 h and 48 h, respectively, compared to the 18 h sample (as illustrated in Figure 1). Colour-coded expression values (log2) are shown, where blue indicates lower expression and yellow indicates higher expression in mutant compared to wild-type (or in wild-type 36 h or 48 h sample compared to 18 h sample). Grey boxes indicate comparisons for which there is no expression value since not all four arrays showed at least one good spot.