Scientists have sequenced the DNA of a frozen horse discovered in Canada’s Yukon Territory in 2003 and discovered the oldest DNA ever sequenced. The new methodologies used by the researchers confirmed that the genus Equus dates back more than 4 million years — twice as long as scientists previously believed.
“Previous to this, the oldest genome ever sequenced was of a 120,000-year-old polar bear — no small feat considering that the half-life of a DNA molecule is estimated to be about 521 years. — Dr. Ludovic Orlando of the University of Copenhagen
The fact that the remains were frozen helped slow the rate of decay. But they also “targeted specific DNA preservation niches,” he said, like the protein called collagen found in the animal’s bones, which is more DNA-rich than other tissues.
“But also we pioneered the usage of what is called true Single Molecular Sequencing that basically reads through molecules as they stand, without further manipulation,” Orlando added.
By tracking a full, single DNA molecule, the team was able to avoid having to “amplify” fragments, which can often introduce errors. The team then compared it against the genome of a 43,000-year old horse, modern domestic horse breeds, and the Przewalski’s horse, which is the last surviving population of wild horses. These full-genome comparisons allowed the scientists to construct “a molecular clock” that revealed benchmarks in the horse’s evolutionary history.
The DNA-decoding methods used on the ancient horse could potentially be used on early human ancestors next and could reveal how human species like Homo heidelbergensis may have been related genetically to Homo neandertalensis and modern humans.