The popularity of DNA testing to unearth one’s family roots has never been greater. As the science gets more precise and less expensive, using DNA as a genealogical tool has become a national pastime, particularly among baby boomers who feel the pangs of mortality.

I’ve covered this technology in the past, but when my Tech View collaborator, Rob Kay, presented me with his own family mystery, I thought it was time to visit the subject again.

The story begins in San Francisco in the 1950s. Growing up there, Rob and his siblings were close with their cousins, who lived in the same Sunset District neighborhood. He was particularly close to his cousin Phil, who is the same age.

Both Phil’s mom (Ruth) and Rob’s mom (Carla) were close friends, German-Jewish immigrants whose families had settled in San Francisco. Growing up, the children were told by their mothers that they were related, without ever explaining the precise genealogical connection.

After Rob’s and Phil’s moms died, the two cousins remained in touch via Christmas cards and holiday updates on the families. Earlier this year Rob paid Phil a visit to his home in Albuquerque, N.M., and they started questioning each other about exactly how they were related. Both scrutinized each other’s family trees, but there didn’t seem to be an obvious connection.

They began to speculate whether their purported family ties really existed. Had their moms, who were new to America, invented a kinship that didn’t exist?

“Phil and I began to wonder,” said Rob.

Enter a DNA testing company called Family Tree DNA, which says on its website that it can “confirm family lore and traditions.” Founded in 2000, FTDNA does all the testing for the highly acclaimed National Geographic Genographic program and, notably, doesn’t resell its data to Big Pharma.

Rob spoke with the FTDNA founder, Bennett Greenspan, who recommended that Phil, Rob and Rob’s brother Stephen get tested using their “Family Finder” product, which has an effective “family matching” system that can validate what the company refers to as “uncertain relationships.” “This allows you to see how much common DNA (from both sides of your family) that you share with an individual. Family Tree DNA also sifts its database of more than 829,000 people and comes up with more potential matches.

The Family Finder test utilizes “autosomal” data inherited from both parents and provides information on relationships as well as ethnic and geographic origins. The company also offers other tests that can focus specifically on maternal or paternal lines. Prices range from a holiday savings price of $59 for Family Finder to the $300 range for more extensive tests.

Greenspan said that for cases in which customers might be distant cousins, testing two relatives (as with the two Kay brothers) was important because even siblings will inherit various amounts of DNA, and the odds are better to determine a distant relative by looking at more than one family member.

The verdict

After several weeks all three kits were tested and the verdict was in.

Both Rob and Phil shared 185 centimorgans (a unit for measuring genetic linkage) and, just as significantly, a large (35-centimorgan-long) block of autosomal DNA. Rob’s younger brother, Steve, also shared common blocks of DNA with Phil, but not in the same quantity.

“I think you’re related,” said Greenspan, “most likely third cousins who share great-great-grandparents.”

Mike Meyer, formerly internet general manager at Oceanic Time Warner Cable, is now chief information officer at Honolulu Community College. Reach him at mmeyer@hawaii.edu.