Identical twins, identical DNA, different ancestry results? We put three kits to the test

MOBILE, Ala. (WALA) - Caroline and Camille Clarke are 7-year-old first-graders at Hutchens Elementary School in Mobile. Their favorite subject is science.

It shouldn’t be a surprise – they’re identical twins.

So the results of DNA tests should be exactly the same for both girls, right? To find out, FOX10 News had each girl take three of the most popular DNA ancestry kits on the market – Ancestry.com, 23andMe, and National Geographic.

Mother Lauren Clarke had an idea of what to expect, based on what she knows of her family history and an ancestry DNA test her father took.

“My dad’s side was all European, so basically from the U.K,” she said several months ago as her daughters were spitting into vials. “So, I’m interested to see. I know his family is Clarke, which is traditionally Irish, Scottish. So, I’m interested to see what theirs come back as.”

Indeed, all three tests pegged the twins’ ancestry in that region of the world. But a closer look reveals nuances. Ancestry.com lists the girls as 63 percent England, Wales and Northwestern Europe, and 37 percent Ireland and Scotland.

But 23andMe breaks it down a little differently. It says about 60 percent British and Irish, while listing other regions in Europe separately. The results from NatGeo, meanwhile, turn up something the other two didn’t. It finds Caroline and Camille have 2 percent DNA from northern India.

“We actually talked about how there was just a little variation,” Lauren Clarke said. “That was interesting.”

Perhaps more surprisingly, small differences showed up even within the same company.

For instance, 23andMe indicated that Camille is 63.2 percent British and Irish. But Caroline was only 59.9 percent British and Irish. The test found nearly twice as much Italian DNA in Camille than it found in Caroline.

Confused by discrepancies

Those discrepancies confused the Clarkes.

“Yeah, which you would think would have been exactly the same, given that they have identical DNA,” Lauren Clarke said.

Her husband, Joshua Clarke, agreed.

“It should be. You would think,” he said. “But, I don’t know; we talked about that. We thought, well, maybe it’s … the way that their lab tests the sample, or maybe there was, you know, more of a sample.”

Representatives from 23andMe say the differences in results come down to how the DNA is analyzed. The analysis involves segmenting chromosomes into short pieces, or “windows.”

“Between identical twins, not every window will start and end at exactly the same place, which may result in small variations between the two results even though the DNA is identical,” the company said in a statement.

All ancestry DNA tests work on the same principle – examining the DNA for markers called single-nucleotide polymorphisms, or SNPs. By comparing a customer’s DNA, researchers can find markers that are common in people from specific parts of the word.

But different companies have different ways of making that determination. And there are many factors that can influence the results. For instance, someone might have an ancestor from southern Europe who mixed with people from the Middle East hundreds of years ago. This can throw off the results.

Different companies also have different “reference populations” used to affix a person’s ancestry. The more people in the database, the more accurate and refined the results become. But just because someone has a marker common to a certain population does not guarantee he or she had ancestors from that region. Conversely, someone may have ancestors from a region even if he or she does not have that marker.

“From a medical perspective, we definitely consider at-home ancestry tests as being for entertainment only,” said Dr. Anna Hurst, a medical geneticist at the University of Alabama at Birmingham. “There are chances and times when people should expect unexpected results.”

Not an exact science

A close look at the ancestry DNA results offers a flavor of the fluidity of analysis. For instance, that 63 percent England, Wales and Northwestern Europe finding reported by Ancestry.com for the Clarke girls is not as exact as it may sound. The fine print reveals that 63 percent is merely the most likely result in a range from 62 percent all the way to 80 percent.

Reports of small amounts of DNA from various places are less certain. The 23andMe report suggests that the Clarke girls have small amounts of DNA from Scandinavia, Finland, Italy, Spain and Portugal.

But that is at the website’s default setting of a 50 percent confidence level. Raise that setting to 90 percent, and that variety goes away. At that highest level of confidence, 23andMe can only be certain that Caroline’s DNA is 0.6 percent French and German. At the 50 percent setting, it is 14.2 percent.

So, these are all just estimates. And it’s not an exact, precise science.

Hurst suggested taking the results of any ancestry DNA kit with a grain of salt.

“So, these are all just estimates,” she said. “And it’s not an exact, precise science.”

For the Clarke parents, the experience was illuminating. They said they might even start doing non-DNA research, gathering records of their ancestors to find out more about their family history.

For the Clarke children? Maybe, they’ll appreciate it in the future. Now, not so much.

“Did you like that? Was that fun?” a reporter asked Camille.

She just shook her head.

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