Global expression analysis in pea aphid development. A) Micro-photographs of the four stages analysed in this work where the scale bar represents 200 μm in all photographs to allow for size comparison. The microphotographs show just one embryo stage among those belonging to the corresponding groups (see Table 1 for detail). The performed comparisons, early embryos (EE) versus intermediate embryos (IE), intermediate versus late embryos (LE) and late embryos versus first larval stage (L1) are labelled, respectively, in rose, violet and light blue. B) Unsupervised hierarchical clustering (generated by an average linkage method with euclidean distance and no leaf order optimization) of 50% of transcripts (12,005) showing the higher standard deviation among all the samples. 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). C) The Venn diagram of the 3945 genes showing significantly differential expression in the three comparisons (comparison colour code as in Figure 1A). 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.