World's oldest genome sequenced from 700,000-yr-old horse DNA

Scientists have sequenced the world's oldest genome from a 700,000-year-old horse, analysing DNA molecules preserved in bone-remnants of the frozen prehistoric creature.
Scientists at the Centre for GeoGenetics at the Natural History Museum of Denmark (University of Copenhagen) sequenced and analysed short pieces of DNA molecules preserved in bone-remnants from a horse that had been kept frozen for the last 700,000 years in the permafrost of Yukon, Canada.
By tracking the genomic changes that transformed prehistoric wild horses into domestic breeds, the researchers have revealed the genetic make-up of modern horses with unprecedented details.
DNA molecules can survive in fossils well after an organism dies. Not as whole chromosomes, but as short pieces that could be assembled back together, like a puzzle.

Sometimes enough molecules survive so that the full genome sequence of extinct species could be resurrected and over the last years, the full genome sequence of a few ancient humans and archaic hominins has been characterised. But so far, none dated back to before 70,000 years.
Now, Dr Ludovic Orlando and Professor Eske Willerslev from the Centre for GeoGenetics have beaten this DNA-record by about 10 times.

Thereby the two researchers - in collaboration with Danish and international colleagues - have been able to track major genomic changes over the last 700,000 years of evolution of the horse lineage.
First, by comparing the genome in the 700,000 year old horse with the genome of a 43,000 year old horse, six present day horses and the donkey the researchers could estimate how fast mutations accumulate through time and calibrate a genome-wide mutation rate.

This revealed that the last common ancestor of all modern equids was living about 4.0-4.5 million years ago. Therefore, the evolutionary radiation underlying the origin of horses, donkeys and zebras reaches back in time twice as long as previously thought.
Additionally, this new clock revealed multiple episodes of severe demographic fluctuation in horse history, in phase with major climatic changes such as the Last Glacial Maximum, some 20,000 years ago.
The study also found that the Przewalski's horse population from the Mongolian steppes became isolated from the lineage leading to the present day domesticated horses about 50,000 years ago.
As the scientists could detect similar levels of genetic diversity within the Przewalski's Horse genome than in the genomes of several domestic breeds, this suggests that the Przewalski's Horses are likely genetically viable and therefore worthy of conservation efforts.

The results are published in the journal Nature.