Last month's publication of the draft genome sequence of the mouse (see Highlights and In the news articles on p4) opened up a rich and long-awaited new resource for researchers interested in finding out the function, location and number of human genes. The draft sequence of the human genome was the first important step towards this goal. However, many hypotheses can only be tested effectively by comparing our genome with those of informative species such as the mouse. Take, for example, the idea that humans can be made from only 30,000 genes: although their genome is 14% smaller, mice also seem to make do with around that number of translated transcripts, 99% of which are directly homologous to our genes.

If the hope is that mice will tell us how to build a mammal, it will take an even more closely related species to explain what makes us human, although a comparison between mouse and human non-coding regions is likely to provide some useful clues. In their review on p20, Maynard Olson and Ajit Varki discuss the rewards that could be reaped from the imminent large-scale sequencing of the genome of the common chimpanzee — our closest living relative. This project, which started only five years ago, will allow us to test evolutionary hypotheses about our divergence from the great ape lineage as well as highlight those subtle genomic differences that underlie the different susceptibility of humans and chimps to infection and disease. The premise of this project runs somewhat counter to the common perspective that chimps and humans are remarkably similar. However, the project is justified by the hope that many scientific and medical problems will be solved as a result of it.