Horse Fossil Yields Astonishingly Old Genome

Horse Fossil Yields Astonishingly Old Genome—Are Similarly Ancient Human Genomes Next?
By Kate Wong | June 26, 2013

Horse fossil dating to around 700,000 years ago has yielded the oldest complete genome yet. Image: D. G. Froese

Horse fossil

Horse fossil dating to around 700,000 years ago has yielded the oldest complete genome yet. Image: D. G. Froese

Researchers have recovered DNA from a nearly 700,000-year-old horse fossil and assembled a draft of the animal’s genome from it. It is the oldest complete genome to date by a long shot–hundreds of thousands of years older than the previous record holder, which came from an archaic human that lived around 80,000 years ago. The genome elucidates the evolution of modern horses and their relatives, and raises the question of whether scientists might someday be able to obtain similarly ancient genomes of human ancestors.

Ludovic Orlando of the University of Copenhagen and his colleagues extracted the DNA from a foot bone found at the site of Thistle Creek in Canada’s Yukon Territory in permafrost dating to between 560,000 and 780,000 years ago, which falls within the so-called early Middle Pleistocene time period. They then mapped the fragments of DNA they obtained against the genome of a modern horse to piece together a draft of the ancient horse’s genome.

Comparing that sequence to the genomes of a 43,000-year-old horse, a donkey, five modern domestic horses and a modern Przewalski’s horse (a type of wild horse native to Mongolia), the researchers were able to gain insights into some key aspects of horse evolution. Their findings indicate that the last common ancestor of the members of the genus Equus—which includes modern horses, donkeys, asses and zebras, along with their extinct relatives–lived some 4 million to 4.5 million years ago, double the estimate suggested by the oldest unequivocal Equus fossils. The results also allowed the team to chart the demographic history of horses over the past two million years, revealing how the population waxed and waned as climate shifted and grasslands expanded and contracted. In addition, the researchers identified several genome regions in modern horses that seem to have been targeted by natural selection acting to promote advantageous gene variants related to immunity and olfaction, as well as a number of genome regions that may have undergone selection related to domestication. A report detailing the study will be published in the June 27 Nature.

Read full article at Scientific American

Source: Scientific American Blogs: Horse Fossil Yields Astonishingly Old Genome—Are Similarly Ancient Human Genomes Next?

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