Where did I come from?
One of the popular uses of recreational genotyping is ancestry determination. Everyone inherits mitochondria only from our mothers, who got it from their mothers, and so on. Your mitochondrial DNA is a good match for your greatnth-grandmother, and people will sell you stories about where she came from. In men, the Y chromosome does the same job for male-line ancestry.
When you go back even 50 generations (eg, very roughly to the settlement of New Zealand, or the Norman Conquest), you have approximately a million billion ancestors, obviously with rather a lot of overlap. You might wonder if the single pure female line ancestor was representative, and how informative she was about your overall ancestry.
In a new paper in the American Journal of Human Genetics, researchers looked at what you’d conclude about ancestry from the mitochondrial DNA compared to what you’d conclude from the whole genome. They weren’t trying to get this very precise, just down to what continent most of your ancestors came from. This is what they found:
Continental-ancestry proportions often varied widely among individuals sharing the same mtDNA haplogroup. For only half of mtDNA haplogroups did the highest average continental-ancestry proportion match the highest continental-ancestry proportion of a majority of individuals with that haplogroup. Prediction of an individual’s mtDNA haplogroup from his or her continental-ancestry proportions was often incorrect. Collectively, these results indicate that for most individuals in the worldwide populations sampled, mtDNA-haplogroup membership provides limited information about either continental ancestry or continental region of origin.
The agreement was better than chance — there is some information about ancestry from just your greatnth-grandmother — but not very good. It wasn’t even a particularly severe test, since the samples were a set that had been previously selected to expand the diversity of genome sequencing and were deliberately spread out around the world. In a random group of young adults from London or New York or Rio you’d expect to do worse.
Thomas Lumley (@tslumley) is Professor of Biostatistics at the University of Auckland. His research interests include semiparametric models, survey sampling, statistical computing, foundations of statistics, and whatever methodological problems his medical collaborators come up with. He also blogs at Biased and Inefficient See all posts by Thomas Lumley »
Here’s an anecdote about how non-representative DNA ancestry can be…
Oscar Kightley (Samoan) and Nathan Rarare (Maori) did a show where they looked at their DNA ancestry in
“Made in Taiwan”
http://www.nzonscreen.com/title/made-in-taiwan-2006
(Where the whole thing is on-line.)
Oscar’s male-line DNA ancestry was from Asia around the Himalaya area and Nathan’s, whose (IIRC) great grandmother was from Cornwall had American mDNA ancestry.
10 years ago
I thought of this too. From memory both of them were unaware that their Pakeha/Palagi ancestors were anything other than English.
10 years ago