The bone came from an ancestor of modern horses that lived in the west-central Yukon Territory in northern Canada. The bone was very well preserved in the permafrost after the animal died and analysis showed that it still had small samples of connective tie and blood-clotting proteins, things that are usually long gone from ancient bones.
The well-preserved bone excited the study's co-author Dr. Ludovic Orlando of the University of Copenhagen, so he decided to try and extract DNA from a fragment of the bone. Their first method of putting the bone through gene sequencing did not produce great results, so they instead used technology that could analyze the single molecules of DNA.
Using a genome sequence of an existing horse as an example, the scientists had to sift through a lot of data to figure out which DNA belonged to the horse and which belonged to bacteria. They were only able to collect enough DNA to cover about 70 per cent of the animal's genome, but it was enough to reveal details about the horse and figure out the evolutionary history of modern-day horses and zebras.
The presence of Y chromosomes showed that the bone belonged to a male horse. It was about the size of our current Arabian horses and likely didn't have the same genes for large muscles like some of today's breeds have that make them good for racing. They also came to the conclusion that horses and donkeys started traveling down different evolutionary paths about four million years ago.
The techniques used to map the genome could also be used on samples other than frozen fossils, and could maybe even be used to map million-year-old animal genomes!