ABSTRACT
The ability to analyse the expression of thousands of genes in one experiment is revolutionizing the study of gene transcription. Many microarray platforms now exist that allow the determination of transcript expression levels for entire genomes such as yeast and for at least ail of the annotated genes in human and mouse genomes.1'5 Indeed, with the advent of tiling arrays the transcription patterns across whole human chromosomes have recendy been investigated with many surprising results.6'8 The data from such experiments allows the determination of gene groupings that are coexpressed during developmental pro cesses or in response to exposure of cells to specific treatments and there are now many hun dreds of these types of analyses in the literature.
