I'm writing a story which is intended to be mostly realistic and historically accurate, but with one character who is biologically immortal. She is born in a Pictish/Caeldonian/Celtic village in modern-day Scotland, and by the time the story begins, she lives in a small town in the Pacific Northwest of the United States. The town is more or less run by a secret cult which worships her and helps protect her secret from the outside world.
My question is centered around a character who is part of this cult. While fleshing him out, I had the idea that he could be a direct descendant of the immortal character. While doing research, I learned that Celtic (not sure about Pictish or Caeldonian) society was somewhat matriarchal, and genealogy was "recorded" (though not in writing in this context) along the matrilineal line. This made me think the descendant character could be from a direct matrilineal line, and when I looked into DNA testing, I found a source saying that mtDNA testing is useful for following the matrilineal line specifically.
I'm now trying to come up with a plausible scenario that explains how the cult tracked down the descendant character. The story takes place in 1987, and the cult needs to have found the descendant character by then. I found a source saying that mtDNA was available during the 1980s, but also various sources saying that commercial DNA testing was not widely available until later. I also found a source which, based on my reading, says that mtDNA testing is most effective as a way of proving or disproving an existing hypothesis about matrilineal descent.
In my ideal case, the cult has information along these lines:
- Reliable information about the immortal character's descendants for the first 200 years of her life, based on her memory
- Some gaps following this
- Some hypotheses about possible descendants from 300-600 AD (along with reliable records for each candidate's descent)
- Some gaps
- More hypotheses/reliable information (in isolation), etc.
mtDNA testing would then ideally let them fill in these gaps in a way that would require a bit of luck, as well as a lot of work to collect DNA samples, but not be completely implausible.
(Edit to pose only a single primary question)
Based on all of this context, I particularly want to know: would mtDNA testing make it easier to establish ancestry between the immortal character and a direct matrilineal living descendant of hers, assuming that the cult is already aware of him or her as a potential candidate based on known records?