A number of array-based technologies have been developed over the last several years, and technological development in this area is likely to continue at a brisk pace. These technologies include DNA, protein, and combinatorial chemistry arrays. So far, DNA arrays designed to determine gene expression levels in living cells have received the most attention. Since DNA arrays allow simultaneous measurements of thousands of interactions between mRNA-derived target molecules and genome-derived probes, they are rapidly producing enormous amounts of raw data never before encountered by biologists. The bioinformatics solutions to problems associated with the analysis of data on this scale are a major current challenge.

Like the invention of the microscope a few centuries ago, DNA arrays hold promise of transforming biomedical sciences by providing new vistas of complex biological systems. At the most basic level, DNA arrays provide a snapshot of all of the genes expressed in a cell at a given time. Therefore, since gene expression is the fundamental link between genotype and phenotype, DNA arrays are bound to play a major role in our understanding of biological processes and systems ranging from gene regulation, to development, to evolution, and to disease from simple to complex. For instance, DNA arrays should play a role in helping us to understand such difficult problems as how each of us develops from a single cell into a gigantic supercomputer of roughly 1015 cells, and why some cells proliferate in an uncontrolled manner to cause cancer.