Am Af

<0.25 0.33 0.5 1 2 3 >4 Expression level

▲ EXPERIMENTAL FIGURE 15-5 DNA microarray cluster analysis detects global changes in transcription in Drosophila development. The life cycle was divided into about 70 periods from early embryos through aged adults. The mRNA was extracted from animals at each period, converted into fluorescence-labeled cDNA, and hybridized to microarrays representing about 5000 genes. Computer analysis of the original microarray data grouped genes showing similar changes in expression relative to a standard reference sample. (See Figure 9-35 for general protocol of DNA microarray experiments.) The three panels shown represent only a small fraction of the genes in the microarray. Each very narrow row in a panel represents a different gene. General periods are labeled E (embryogenesis), L (larval), P (pupal), and A (adult, male or female). Each vertical line represents one of the 70 developmental periods. Yellow indicates an increase in transcription compared with the reference sample; blue, a decrease in expression; and black, no significant change in expression. Genes are grouped, or "clustered," because they have similar rises and falls in RNA abundance during development. Clusters often reveal genes involved in similar processes. The three clusters here are mitochondrial protein genes (top), ribosomal protein genes (middle), and genes involved in the cytoskeleton and neural development (bottom). The clustering of a gene of unknown function with some of known function provides a hypothesis about the function of the former. [Adapted from M. Arbeitman et al., 2002, Science 297:2270.]

functional inactivation cause particular abnormal phenotypes can be grouped into sets; each member of a set presumably controls the same signals or events. The regulatory relations among the genes in the set—for example, the genes that control muscle development—can then be worked out.

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