What is it??
Affymetrix – thousands, (or soon with hundreds of thousands) of spots, each spot containing a different DNA oligomer.
Compare cells before and after perturbation:
Techniques include microarray, functional annotation techniques.
Group together genes with similar patterns of expression:
Clustering can be thoughtof as forming a phylogenetic tree of genes or tissues. Genes arenear each other on the "gene tree" if they show a strong correlationacross experiments, and tissues are near each other on the "tissuetree" if they have similar gene expression patterns.