For generations, cross-referencing tombstones at the cemetery and vital records was required to unlock your lineage. But now, you can easily uncover some of the mystery of your family tree with DNA. Consumers like Larry Guernsey are giving the service as gifts. "I thought it would be a good Christmas present," Guernsey said. The $99 DNA test uses a saliva sample to trace family history. Here's how one company that provides the service, Ancestry, says it works: "A simple test can reveal an estimate of your ethnic mix… like if you're Irish or Scandinavian, or both." For Guernsey his curiosity...