Dr. Erlich began with one man from the database. He got the Y chromosome’s short tandem repeats and then went to genealogy databases and searched for men with those same repeats. He got surnames of the paternal and maternal grandfather. Then he did a Google search for those people and found an obituary. That gave him the family tree.
“Now I knew the whole family,” Dr. Erlich said. And it was so simple, so fast.
Search of DNA Sequences Reveals Full Identities - NYTimes.com