Now that whole genomes have been sequenced, a group of scientists has geared up for the next phase: identification and classification of newly discovered coding regions. The DNA microchip, developed just a few years ago, has already become a standard tool in the geneticist’s repertoire. With genomic sequence in hand, the researcher can synthesize all the genes in an organism — or even just fragments of them — and then dot them in a regular pattern on a glass slide. But for many organisms, up to 40 percent of the DNA sequences on the chip have no known function. The challenge is to design probes that make a particular spot stand out. It is a daunting task. According to George Church, Harvard Medical School professor of genetics, approximately 600,000 bacterial genes will be sequenced in the coming two years. Eric Rubin, Harvard School of Public Health assistant professor of immunology and infectious disease, and Church have each independently developed a new method that marries the best of microchip analysis and another technique, transposon mutagenesis, to evaluate the function of newly sequenced genes.