I have foolishly accepted to act as an advisor to my uncle (on my mother's side), and find that I am quite unprepared to do so.
He is trying to follow up a family tradition that his x-GF (all on his paternal line) emigrated to southern Germany from Switzerland in 1589. His last name is concentrated in one village in Germany, whereas the name is quite prevalent throughout Northern Switzerland (with concentrations around Zurich and around Winterthur/St. Gallen). I have been in email contact with a person in Switzerland who shares my uncle's last name and participated in a largish DNA study on Ancestry.
According to this gentleman, there are two unrelated groupings of the family name, which correspond to the geographic distribution. The Winterthur members of the family are related to each other, but not to the Zurich group, and vice versa. The Southern German group was not represented in the study.
My uncle would like to test the family tradition, but he asked me for advice about the DNA tests. It sounds like a Y-DNA test would be most appropriate to prove descendance along the male line. If there is a match with either the Zurich or the Winterthur strain, then that would confirm the family tradition. If not, the tradition looks a bit shaky.
Through the aforementioned gentleman, I think I can get access to one person from each group, but I am not sure if that is a good idea.
On one hand, is it possible to link into the existing study? Since most likely the genetic split would have happened more than 400 years ago, I am not sure what a match or absence thereof would prove.
On the other hand, I have done my own DNA through 23AndMe and was told my Y-haplogroup. The analysis says that this particular haplogroup arose about 10,000 years ago and is shared by something like 20% of all European males. This seems to indicate that a Y-DNA test might not be all that useful, either.
I have been reading that familytree.com has a proper Y-test, but I do not understand the differences, and I am totally confused at this point.
What is the best DNA test to study whether a male 400 years ago belonged to one of two particular families if all one has is 21st century data?