Rose-colored goggles.

of the disease-associated sites), the mouse sequence was the same as the human disease-associated sequence. Moreover, in 23 of these, there is documentation of a cause-and-effect relationship between the mutation and disease in humans (Mouse Genome Sequencing Consortium, 2002). This unexpected finding is important because it implies that the harmfulness of a mutation can depend on the biochemical context in which it occurs. A mutation that causes disease in humans may not have been harmful in the ancestor of the mouse because of other changes occurring in the rodent lineage that served to buffer the mutation’s effects. As with any new genome sequence, the initial report of the mouse genome (Mouse Genome Sequencing Consortium, 2002), together with companion papers (Dermitzakis et al, 2002; The FANTOM Consortium and the RIKEN Genome Exploration Research Group Phase I and II Team, 2002; Wade et al, 2002), only scratches the surface of the information made available to biologists through sequencing of the mouse genome. Comparison of human and mouse genomes is certain to yield important new insights in the near future as well as provide a rich source of testable hypotheses for experimental biologists working in both rodent and primate systems. ’ Austin L Hughes is at the Department of Biological Sciences, University of South Carolina, Columbia, SC 29208 USA.