Mice and men share about 97.5 per cent of their working DNA, just one per cent less than chimps and humans. The new estimate is based on the comparison of mouse chromosome 16 with human DNA. Previous estimates had suggested mouse-human differences as high as 15 per cent. The new work suggests that neither genome has changed much since we shared a common ancestor 100 million years ago. "The differences are going to be few rather than many," says Richard Mural of Celera Genomics, the Maryland company that compared the mouse chromosome with human DNA. "Perhaps 100 million years separating...