Developmental gene expression analysis in pea aphid. A) Hierarchical clustering (generated by an average linkage method with euclidean distance and no leaf order optimization) on the 368 developmental genes present on the microarrays (out of the 387 annotated by Shigenobu et al.). The colour chart indicates expression intensities using a base 2 logarithmic scale: blue and red represent, respectively, lower (2.0) and upper (16.0) expression intensities (see bottom panel legend). On the right of the cluster, genes showing significant differential expression in at least one of the comparisons are indicated: in green, 27 homeobox-containing genes; in red, 32 signalling pathways genes; and, in black, 59 other developmental genes. B) The Venn diagram, showing the 118 developmental genes with significantly differential expression in the three comparisons (comparison colour code as in Figure 1A) analysed in this study. Numbers in red identify the genes increasing in expression during development; in dark blue, the genes decreasing in expression during development; and, in black, the genes found to be significant in two or more groups where the expression changes are not varying in the same direction in the different comparisons.