Ancestry DNA Tests Don't Always Find What We Expect : Shots - Health News Popular DNA ancestry tests don't always find what people expect. That is because of how DNA rearranges itself when egg meets sperm — and the quirks of genetic databases.

My Grandmother Was Italian. Why Aren't My Genes Italian?

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Chances are you have seen an ad for a test to find out about your ancestry. Maybe you got a kit for Christmas, and now you're waiting for your results. So what do you need to know when you open these results? Health editor Gisele Grayson and her mother help us explain.

GISELE GRAYSON, BYLINE: History professors never really retire.

CARMEN GRAYSON: Are you clicking view your reports, Gisele?

G. GRAYSON: All right. All right. View my report.

I'm with Carmen Grayson, my mother, who taught at Hampton University for 25 years.

C. GRAYSON: World history, military history, American history, Greece and Rome history (laughter). Do you want me to stop?

G. GRAYSON: We're opening genetic test results from a company called 23andMe. Mom recently became interested in what our genes could tell us about her family's migrations to Washington from Canada, from France and from Italy. We got some good information, and a puzzle. Last fall, we used a different company, Helix, that works with National Geographic. Mom's results?

C. GRAYSON: Thirty-one percent from Italy and Southern Europe.

G. GRAYSON: Did you expect that?

C. GRAYSON: Definitely. Two grandparents, both born in Italy...

G. GRAYSON: And lived there as far as you can trace back. They gave birth to my mom's mom, Gisella D'Apollonia. But my Helix results had no Italian and Southern European category. Was I switched at birth?

C. GRAYSON: You were born with a lot - a lot - of black, curly hair.

G. GRAYSON: So she was sure it was me in the hospital nursery. And we do kind of look alike. So we decided to get this second opinion from 23andMe.

C. GRAYSON: My top category is Italian, 11 percent. Do you have any Italian?

G. GRAYSON: I have 1.6 percent Italian.

C. GRAYSON: There you go.

G. GRAYSON: (Laughter). All right.

C. GRAYSON: My daughter.

G. GRAYSON: But, really, how could I have an Italian grandmother and little to no Italian in my results? We put the question to geneticist Aravinda Chakravarti at Johns Hopkins.

ARAVINDA CHAKRAVARTI: That's surprising, but it may still be within the limits of error that these methods have.

G. GRAYSON: The science is good, he says, but the ways the companies analyze genes leave room for interpretation.

CHAKRAVARTI: They would be most accurate at the level of continental origins, and as you go to higher and higher resolution, they would become less and less accurate.

G. GRAYSON: As in my case. The results got me to Europe, just not Italy. A few things are at play in this ancestry analysis. First is our actual genetic material. The rule is you get 50 percent of your DNA from each parent. But Elissa Levin, with the company Helix, says a process called recombination means each egg and each sperm carries a different mix of your parents' genes.

ELISSA LEVIN: When we talk about the 50 percent that gets inherited from Mom, there is a chance that you have a recombination that just gave you more of the Northwest European part rather than the Italian part of of your mom's ancestry DNA.

G. GRAYSON: Then she says that companies compare your DNA to samples they have from people around the world who have lived in a certain area for generations.

LEVIN: What are the specific markers? What are the specific segments of DNA that we're looking at that enable us to identify, you know, those people are from this part of Northern Europe, or Southern Europe or Southeast Asia?

G. GRAYSON: And as the companies get more samples, they'll get more accurate. Also humans have migrated and mingled for tens of thousands of years, and most people have a DNA mix. So - says Robin Smith, with 23andMe - a computer algorithm does some sophisticated guesswork.

ROBIN SMITH: Let's say a piece of your DNA looks most like British and Irish, but it also looks a little bit like French, German. Well, based on some statistical measures, you know, we would decide whether to call that as British, Irish or French, German. Or maybe we'd go up one level and we call it North Western European.

G. GRAYSON: Could that explain my case?

SMITH: It was a little surprising to me, yeah. But, you know, in looking at, you know, the fact that you had some Southern European and the fact that you had some French, German, the picture became a little bit clearer to me.

G. GRAYSON: So for now my Italian grandmother doesn't show up in these tests. No matter, all the researchers say, let the results add to your life story. The DNA is just a piece of what makes you you. Gisele Grayson, NPR News.

MARTIN: And just a note - the company 23andMe mentioned in this story is an NPR funder.

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