DNA fragments over time, largely because of depurination, making it hard to analyze very old samples. The fragmentation rate is temperature-based; DNA from samples recovered from permafrost tends to be less fragmented than DNA from samples found elsewhere. Recently, for example, scientists were able to reconstruct the genome of an approximately 700,000 year old horse from a sample in Canada’s Yukon Territory. Until now, however, scientists have only been able to generate sequences from non-permafrost samples about 120,000 years old or younger.
Meyer and his colleagues studied a bone sample from a Middle Pleistocene cave bear (Ursus deningeri). The sample, found at Spain’s Sima de los Huesos cave site, was more than 300,000 years old. The researchers believed they could recreate the cave bear’s genome by improving the method of DNA extraction.
Read more at: Phys.org