Page last updated at 18:34 GMT, Wednesday, 19 November 2008

Mammoth's genome pieced together

By Paul Rincon
Science Reporter, BBC News

Mammoth hair (SC Schuster)
Mammoth hair has been preserved in the Siberian permafrost

A US-Russian team of researchers has pieced together most of the genome of a woolly mammoth, Nature journal reports.

The experts extracted DNA from samples of mammoth hair to reconstruct the genetic sequence of this Ice Age beast.

Though some stretches are missing, the researchers estimate that the genome is roughly 80% complete.

The work could provide insights into the extinction of the mammoth and also resurrects questions about the viability of cloning long-dead species.

The scientists were aided in their task by the fact that several deep-frozen carcasses of woolly mammoths have been dug out of the permafrost in Siberia.

These conditions are ideal for the preservation of hair, which is a preferred source for the extraction of ancient DNA.

Hair today

If genetic material survives in a sample of hair, most of it will belong to the animal that hair is from.

By contrast, when researchers try to extract ancient DNA from bone, it is often swamped with DNA from fungi and bacteria.

The researchers used hair samples from two mammoth specimens recovered from the permafrost.

Lyuba the baby mammoth (Bernard Buigues)
Many frozen specimens have emerged from the Siberian permafrost

Once the researchers had extracted the DNA, they had to estimate how much of it actually came from the mammoth. So they mapped their genome sequence on to that of an African elephant - the mammoth's close relative.

Analysis of the draft sequence revealed that the genome of a mammoth differs from that of an African elephant by just 0.6%.

This is about half the difference between the genomes of a human and a chimpanzee.

It is a curious observation, given that the evolutionary split between the African elephant and the mammoth happened even earlier than the break between the human and chimpanzee lineages.

This seems to suggest that genomes evolve more slowly in elephants (including mammoths) than in humans and great apes. Why this should be the case, though, is still a mystery.

The results also show that the mammoth - along with the African elephant - had a larger genome than is typical for placental mammals. The total mammoth sequence is estimated to be about 1.4 times bigger than the human genome.

Back for good?

Enthusiasts have long dreamt of using ancient DNA to bring extinct species back from the dead. But most scientists are doubtful this could ever be achieved.

The changes that creep into an animal's genetic sequence after its death pose a significant challenge.

Mammoth (SC Schuster)
Could the mammoth be brought back from the dead?

"It's a bit like trying to build a car with only 80% of the parts and knowing that some of the parts are already broken," said Jeremy Austin, deputy director of the Australian Centre for Ancient DNA at the University of Adelaide.

"Even if we did have the genome in its entirety, we still have the problem of knowing what is a real mutation versus what is [a] sequencing error or DNA damage. At a genome scale, this in itself is an almost insurmountable problem.

"After this we have the issues of how to construct artificial chromosomes."

Hendrik Poinar, a geneticist from McMaster University in Ontario, Canada, commented: "We have no idea - yet - how many chromosomes mammoths had."

Paul.Rincon-INTERNET@bbc.co.uk

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SEE ALSO
Mammoths moved 'out of America'
04 Sep 08 |  Science & Environment
Mammoth hair produces DNA bounty
28 Sep 07 |  Science & Environment
Baby mammoth discovery unveiled
10 Jul 07 |  Science & Environment
Gene reveals mammoth coat colour
06 Jul 06 |  Science & Environment
Siberian window on the Ice Age
02 Jul 07 |  Science & Environment
Extinct mammoth DNA decoded
21 Dec 05 |  Science & Environment

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