They are so similar to us, in fact, that chimps are more closely related to humans than they are to gorillas. The reason humans and other species look and behave so differently is that they use those shared genes differently. For example, humans have the same genes that mice use to grow a tail during embryonic development. But in humans those genes are never activated, so most of us are born tailless. 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.