Scientists can now add mouse to the list of animals which have had their genetic blueprint decoded. The work was done here in Cambridge at the Sanger Centre, where the human genome was mapped, and at several centres in the US. The work shows that mice have about 30,000 genes, which is about the same number as humans, and people and mice share about 75% of their genes. Mice have slightly fewer chromosomes than us though - we have 23 pairs, but mice have only 20. We should add that the mouse genome has already been sequenced by a private company in the US called Celera, but researchers have to pay to read the sequence. The new sequence from the Sanger centre will be free for everyone to use.