During the past decade, commercial DNA testing has been made available to the public. Tens of thousands of persons in the United States and additional tens of thousands worldwide have purchased DNA tests to identify their paternal, maternal, and biogeographic ancestries. These tests promise to link persons to ancestors and locales in their distant past, but the tests can also have a profound impact on personal conceptions of identity and ethnicity.
It ought to be possible to compare the DNA of a random individual with DNA from around the world to make a call on ethnicity but there are problems with tests of this kind states author Alva Noë.
The answer as to whether a DNA test can tell you your ethnic identity? Yes — and no… In principle, then, it ought to be possible to compare the DNA of an arbitrarily selected individual with DNA from around the world to make a judgment of that individual’s genetic origins.
The full article by Professor Noë gives a very thoughtful overview of this topic.
For further reading and another point of view on DNA testing and ethnicity, there is a very long and in-depth article “Deep Roots” by Jennifer McAndrew that gives even more insight into this subject.