DNA testing companies can’t tell you who your ancestors are, but they can connect you with “DNA cousins,” people whose marker values match your own. Plug your test results into one of these public online databases, and you may just make an ancestral connection.
You can use these databases whether or not you tested with the company that maintains them—in most cases, you’ll just need to set up an account and add your results to your profile first (Ancestry DNA and GeneTree update their customers’ profiles automatically). Note, too, that some testing companies such as Family Tree DNA, which maintains the public Mitosearch and Ysearch databases, offer separate, private databases that their customers can access.
From the December 2009 Family Tree Magazine.