High‐density microarrays for gene expression analysis

Changes in gene expression are associated with many important biological phenomena including morphogenesis and aging, cancer and disease states, and adaptive responses to the environment. To detect these changes, molecular biologists have, over the years, developed a variety of techniques including RNA blots (1), differential display (2), ribonuclease protection assays (3), and reverse transcription-polymerase chain reaction (RT-PCR) (4). Although these methods are effective, being sensitive and accurate, their dependence on gel electrophoresis places an empirical limit on the number of samples that can be simultaneously analyzed. High-density microarrays, first described by Schena et al. (5), provide the important