The few notable exceptions arise due to glitches that activate those tail genes. Scientists expect the mouse to be the workhorse in the effort to understand how genes work. Celera, the leading private gene-sequencing company, began its own mouse effort in April. Mice are important because they are the classic experimental lab animals. They are small, easy to raise in large numbers and reproduce quickly.
Scientists can also deactivate genes in mice, then watch what happens to the mouse without the gene.
Having the complete mouse sequence will also make it easier for scientists to discern the tiny percentage of human DNA that actually makes proteins. Scientists have found that about 95 percent of human DNA is code for nothing. Mice also have 'junk' DNA, but theirs is different. Over the millions of years of evolution since the two species diverged, their useless DNA has gradually mutated. But their working genes have stayed more or less the same, because once Mother Nature hits on something that works, she sticks with it.