The race is on to produce a commercial DNA microarray that covers the whole human genome.

Applied Biosystems of Foster City, California, announced on 22 July that it plans to have a 'whole-genome chip' on the market by the end of the year. In response, Affymetrix, based at Santa Clara, California, and Agilent Technologies in Palo Alto, California, immediately announced that they intend to do the same.

DNA microarrays allow researchers to assess the level of expression of thousands of genes at a time (see page 610), and a single array for the whole human genome would be an important tool, experts say. Scientists will be queuing up to buy the arrays, says John Hogenesch, a molecular biologist at the Genomics Institute of the Novartis Research Foundation in San Diego.

No one knows how many genes there are in the human genome (see Nature 423, 576; 200310.1038/423576a), but the number represented on the arrays under development ranges from 31,000 to 39,000. “I suspect that the companies are making an informed guess and early versions will be a first step — though a great first step,” says Richard Young, a geneticist at the Whitehead Institute for Biomedical Research in Cambridge, Massachusetts.

The three firms are already jockeying for position. Stephen Fodor, chief executive of Affymetrix, points out that his company has been selling custom versions of a single whole-genome array for the human genome to individual clients for several years. Agilent, meanwhile, says that it already has prototypes for its whole-genome chip.

Researchers have more to look forward to from the chip manufacturers. Both Applied Biosystems and Agilent, for example, have plans to make single whole-genome arrays for mouse and rat available next year.

And Affymetrix has developed prototype arrays for the human 'transcriptome', which represents not only each gene in the genome but also all of the variants of individual genes.