The practical result is that teeth, particularly molars — which have more root canal volume and dentin mass than incisors or premolars — are consistently the most reliable sources of ancient DNA from archaeological contexts. For specimens from the Arctic, where the ambient cold also slows degradation, a tooth that has been in the permafrost or in cold storage can retain DNA of sufficient quality for analysis even after many decades or centuries.
Stephen Fratpietro at the Paleo-DNA Laboratory at Lakehead University has worked with ancient DNA samples for many years. The specific analytical challenge with the Fitzjames molar was not simply extracting DNA — it was extracting DNA of sufficient quality and quantity to generate a Y-chromosome profile specific enough to allow meaningful comparison against a living individual. DNA recovered from ancient specimens is typically fragmented — broken into short sequences rather than the long, intact strands found in fresh samples. Working with fragmented DNA requires different analytical approaches than those used in standard forensic or clinical contexts, and the specific laboratory protocols for ancient DNA extraction involve careful contamination control — ensuring that any DNA recovered comes from the specimen itself and not from the hands of the many researchers who have handled it over the years.
Y-chromosome profiling is a particularly useful approach for historical identification for several reasons. The Y chromosome is passed from father to son with minimal change across generations. Unlike the autosomal chromosomes, which are shuffled through recombination with each generation, the Y chromosome is transmitted essentially intact along the paternal line. This means that a man’s Y-chromosome profile is very similar to that of his male-line ancestors and descendants, with only the occasional mutation distinguishing one generation from the next.