All About My Mother

Plowing through church records and birth rolls will only get you so far in reconstructing your family tree. For the really deep stuff, you must look to your genes, and Bryan Sykes, professor of human genetics at the University of Oxford, is there to help you. His company, Oxford Ancestors (motto: "We put the Genes in Genealogy"), can identify portions of your DNA that chronicle an unbroken chain of descent back to the Stone Age. All it takes is a swab from the inside of your cheek and $180.

The DNA in the mitochondria — cell organelles whose...