Is it on or off? The Use of Microarrays in Functional Genomics

At a time when the human genome has nearly been sequenced and the genomes of various organisms have already been completed, there is a plethora of information waiting to be uncovered in the sequences that make up these genes. Despite such initial breakthroughs in terms of discovering the genetic, structural makeup of organisms, a formidable task lies ahead: to be able to determine the functions of all these genetic sequences. As Mark Schena of Stanford University observes, “Understanding human behavior, disease and other health issues thus requires more than just a knowledge of genes and genomes: one must understand the cellular, physiological, cultural and ecological context in which genomic instructions are being read (1). ” Indeed, the billions of DNA bases alone do not directly tell us about the function of genes, cellular processes, and mechanisms of disease. The advent of genomic technologies such as RNA Northern blots, ribonuclease protection assays, and polymerase chain reaction (PCR) has only begun to explore the surface of interpreting this vast sequence information by identifying genes and evaluating gene expression. An inherent limitation to these methods, though, is that these types o