Scientists from the United States and five other nations have published the genetic code for the mouse. They say the feat gives researchers a powerful tool to better understand the genetic basis of human diseases.

Dogs may be man's best friend by tradition, but the mouse is the researcher's best friend. Mice are very similar to humans genetically and quickly reproduce, so scientists can perform experiments on them that they cannot on people.

As a result, the effort to lay out the chemical sequence of mouse DNA has been an urgent goal following the publication of the one for humans early last year. Now, more than one-year ahead of schedule, an international scientific consortium has determined more than 96 percent of this sequence. It is most of the blueprint for a mouse. "This is not Mickey Mouse science," he said. "This is the mouse that roared!"

The director of the U.S. National Human Genome Research Institute, Francis Collins, says the new mouse map appearing in the journal Nature, and the earlier human genome sequence show that 99 percent of the 30,000 mouse genes have a human counterpart. Therefore, the combined information will allow scientists to experiment with mice to learn more about human diseases and devise treatments for them. "Having the genome of the mouse not only shines new and wondrous light into our understanding of this familiar furry animal, but it powerfully illuminates that other mammal that we know best, ourselves," said Francis Collins.

Man and mouse are thought to have split from a common ancestor about 75 million years ago, when dinosaurs still roamed Earth. Despite the obvious differences that have evolved since then, we still share the same general biological structure and functions common to all mammals.

Since genes are the chemical instructions for cells to make proteins to carry out these functions, research consortium member Eric Lander of the Massachusetts Institute of Technology says it is not surprising the two species have such an overwhelming number of genes in common. "So in fact the mouse is a mirror in which we can see the human," said Eric Lander. "Today, we really see the power of having two genomes instead of simply one genome - the power not just for general questions of biology or general matters of evolution, but the power for biomedicine, because we have a much crisper view of what is in the human genome by comparing it to another genome."

Scientists are also working on the genetic blueprints for the dog, cat, chimpanzee, rat, and other species. They say the ability to compare more genomes will propel research on human ailments even faster.

The analysis in Nature magazine shows that the mouse genome is about 14 percent shorter than that of humans. But the longer human genome is not necessarily superior. It is bigger because it is filled with more so-called junk DNA, repetitive sequences that have inserted themselves over time, but which have no known function. The mouse genome, it seems, is better at housecleaning than humans.

Eric Lander says that because the mouse genome is tidier, a side-by-side comparison is helping researchers better understand what parts of the human genome are non-functional. "We had previously said we gave a range of 30,000 to 40,000 as the human gene number," he said. "Now with the benefit of the mouse genome, I think we can say with much greater confidence that the protein coding gene number is in that neighborhood of about 30,000. So in fact with the benefit of the mouse sequence, we have been able to go back and edit the human gene predictions and clean them up a lot."

With all the similarities, the new mouse gene sequence also shows how the animals differ from people. Some groups of genes have expanded in mice, generally those involved in reproduction, smell, and immunity to disease. Scientists do not know why, but biologist Robert Waterston of Washington University in St. Louis speculates that a shorter generation time, lack of visual acuity and verbal ability, and changes in living environment may account for this. "The mouse genome is different and, of course, it is different in important ways," he said. "Otherwise, we would be small, furry animals running around on the floor."

The international public consortium has published its mouse gene map on the Internet, freely available to other researchers. The scientists said the lack of cost would encourage bright young investigators to clear up the many remaining genetic mysteries of life. They would not comment on a competing mouse gene map published by the private Maryland firm Celera Genomics more than one year ago, which is available only to paying subscribers.