700,000-Year-Old Horse Genome Pushes Limits of DNA Survival

Genetic material suitable for sequencing could persist for as many as one million years, predict scientists.

A Przewalskis horse, which represents the last surviving line of wild horses, in Khomyntal, Western Mongolia.

Small pieces of a horses foot bone that were frozen for approximately 700,000 years in the Yukon Territory of Canada have yielded the oldest genome sequence of any species to date.

Scientists unearthed the bone fragments from the Artic permafrost in 2003 and dated the fossils to be between 560,000 - 780,000 years old. Using mass spectroscopy, they found that collagen and other proteins had survived since the Middle Pleistocene and so decided to see if DNA had also endured.

It had, and the resulting genome is nearly ten times older than any DNA previously sequenced, thus breaking the time barrier for the age of DNA viable for such analysis, said study author Eske Willerslev of the University of Copenhagen at a press conference in Helsinki on Wednesday.

Two pieces of the 700,000 year-old horse foot bone, just before scientists extracted the ancient DNA.

While the cold and dry conditions of the permafrost helped keep the DNA intact, the authors also perfected techniques for handling and analyzining the ancient DNA: reports Nature:

They also combined DNA sequencing techniques to get maximum DNA coverage using routine next-generation sequencing with single-molecule sequencing in which a machine directly reads the DNA without the need to amplify it up which can lose some DNA sequences.

The researchers predict that future ancient DNA studies could go even further back in time most likely up to a million years said Ludovic Orlando, a scientist at the University of Copenhagen and co-author on the study. Such a deep look into the evolutionary past obviously offers great perspective as to the level of detail with which we could reconstruct our own origins and the evolutionary history of almost every single species living on the planet, he said.

The study was published in Nature in Wednesday.

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700,000-Year-Old Horse Genome Pushes Limits of DNA Survival