Of course I wonder how reliable the test is. What if there are people groups that have no identifying mutations?
Then you wouldn't be able to identify them from the DNA. This is an issue of resolution rather than reliability though. You can't see EVERYTHING from DNA, but that doesn't mean the information you can infer is unreliable.
It is, however, not 100% perfect.
Or, here's a specific question: the person who was tested has a Jewish ancestor who is half Northern/Eastern European/Ashkenazi and half Sephardic (Portuguese in this case) but the percentage given makes the ancestor about 97% Ashkenazi. Should this be explained as there being no particular Sephardic mutation?
Depends on the test, really. The Ashkenazi and Sephardic are very similar, typically coming out as quite close to Southern Europe (Italy, Greece, Spain) , for perhaps obvious reasons. A cheap test such as the 23andme test, only looks at a small selection of genetic markers and as said, the two groups are very similar to one another. Not sure if there is a definitive indicator that separates them but 23andme may simply not check it.
Or could it mean that the Sephardic ancestors had a lot of Ashkenazi ancestry they didn't know about?
From wiki:
quote:
In the case of Ashkenazi and Sephardi Jews (in particular Moroccan Jews), who are closely related, the source of non-Jewish admixture is mainly southern European. Behar and colleagues have remarked on an especially close relationship between Ashkenazi Jews and modern Italians.
...
"Ashkenazic and Sephardic Jews have roughly 30 percent European ancestry, with most of the rest from the Middle East." He further noticed that "The two communities seem very similar to each other genetically, which is unexpected because they have been separated for so long." Concerning this relationship he points to Atzmon's conclusions that "the shared genetic elements suggest that members of any Jewish community are related to one another as closely as are fourth or fifth cousins in a large population, which is about 10 times higher than the relationship between two people chosen at random off the streets of New York City"
. And should that unaccounted for 3% be supposed to come from a nonJewish ancestor?
Well, as an approximation, it probably suggests not that there is *A* non-Jewish ancestor, but that 3% of the ancestors were non-Jewish.
Also said person has a grandmother who is French. But the percentage of French in his test is minuscule, like 1.2%. Does that mean the French grandmother doesn't know her real genetic background or what?
Well said person only inherited about 25% of said grandmother's genes. Said grandmother is unlikely to have 100% northern European genetic markers (because Europe has had a lot of migration to and fro), and is certain to not have only genes that are characteristic of French.
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