—
## The DNA Methodology: What Was Done and What It Established
The identification of James Fitzjames from the NgLj-2 mandible rested on two parallel lines of work: DNA extraction from the specimen and genealogical research to identify an eligible living descendant.
Stephen Fratpietro at the Paleo-DNA Laboratory extracted DNA from the molar. The DNA was of sufficient quality to generate a Y-chromosome profile — meaning the genetic material preserved in the tooth allowed the researchers to characterize the Y-chromosome sequence, which in males is passed essentially unchanged from father to son across generations. A Y-chromosome profile from a specimen can be compared against Y-chromosome profiles from living men who share a paternal-line ancestor with the specimen’s owner, with any difference between the profiles representing mutations that accumulated across the intervening generations.
The genealogical work was done by Fabiënne Tetteroo, who had been researching Fitzjames’s family history as part of her academic work and her book project about him. Fitzjames’s illegitimate birth, with his paternity attributed to Sir James Gambier, made this research unusual: she had to trace the paternal Gambier line through records that had not been organized around Fitzjames’s connection to it. After tracing the genealogy, Tetteroo identified Nigel Gambier as a living member of the Gambier paternal line — a distant relative whose Y-chromosome profile could be compared against the profile from the tooth.
Nigel Gambier provided a DNA sample. His Y-chromosome profile was compared against the profile extracted from the molar. The profiles matched.
The specific relationship between Fitzjames and Nigel Gambier — described in coverage of the announcement as a second cousin five times removed — is an expression of the genealogical distance between the two men. At that level of relationship, a Y-chromosome match is a significant finding, because the probability of an unrelated person sharing the same Y-chromosome profile decreases as the profile becomes more specific. The researchers concluded that the match was strong enough to establish the identity of the jaw as James Fitzjames’s.