Ancient fragments: mammoth DNA is damaged

FRAGMENTS of DNA from mammoths have been recovered and sequenced, but are too damaged to make cloning the long-extinct creatures possible, an international team has reported.

Unlike earlier research, the DNA this time comes from the nucleus of mammoth cells, not from the energy-producing mitochondria, Dr Alex Greenwood, of the American Museum of Natural History, in New York, said.

Mitochondrial DNA is more plentiful and easier to detect in ancient samples, but nuclear DNA is more revealing and is the type needed for cloning.

Dr Greenwood and colleagues reported in Molecular Biology and Evolution that they recovered and sequenced nuclear DNA from several Siberian and Alaskan mammoths, as well as from extinct ground sloths from Chile and cave bears from Croatia.

The animals had all been preserved after death in permafrost or in very cold conditions, aiding survival of the tissue, but Dr Greenwood said that the longest sequence that it has been possible to recover is about 100 base pairs long - each base pair representing a letter of the genetic alphabet.

"In modern DNA from living species, you can recover sequences hundreds or thousands of times longer," he said. "This shows that the DNA is very fragmented and there is no way to use it to clone a mammoth."

The results do allow mammoths to be compared to elephants. As expected, there are many parallels, with Asian elephants apparently being more closely related to the mammoth than the African variety.

"The next closest relation is the manatee, and the rest are a long way away," Dr Greenwood said.

The mammoths sequenced all come from museum collections, but Dr Greenwood is now working on a mammoth collected on Wrangel Island in Siberia on an expedition two years ago.

He hopes to be able to find fragments of viruses or pathogens among the DNA, in support of a hypothesis that it was disease that killed off the mammoths.