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 the two genomes is not long enough for wholesale rearrangement,” says Mural, or conservation may be necessary to preserve essential functions.

However, Tim Hubbard, head of genome analysis at the Sanger Institute in Cambridge, UK, is sceptical about the significance of the 2.5 per cent difference. He thinks that the genes might in fact all be identical and that differences between species might arise solely through divergence in the “regulatory regions” which switch other genes on and off.


Nonetheless, scientists are hopeful that the close match will enable researchers to unpick much more rapidly the genetic roots of human disease. By “knocking out” genes in mice using genetic engineering, they can learn the gene’s function.

Doppelganger genes

Mural and his colleagues found chunk after chunk of matching DNA in mice and humans. Of the 731 genes they located on the mouse chromosome, only 14 did not have a doppelganger in humans. Likewise, there were only 21 genes in the corresponding regions of human DNA that did not turn up in the mouse.

Unlike its human genome sequence, Celera is publishing the mouse chromosome 16 data openly on the internet. But the remaining mouse data will require subscribers to pay to see it. “We’ve no real plans to publish anything more,” says Mural.

A version of the mouse genome is already available free of charge on the internet, assembled by researchers at publicly-funded institutes around the world. The Sanger Institute is one of the participating institutes and Hubbard claims that the Celera data is inferior.

“We have fewer gaps, and overall our fragments are larger,” he says. He dismisses the Celera paper as little more than a puff for the company: “It’s a taster for what they are selling.”

Journal reference: Science (vol 296, p 1661)