MINNEAPOLIS (WCCO) — DNA testing kits were among Amazon’s bestsellers during last year’s holiday shopping season, and with popularity expected to keep growing, Dr. Heather Zierhut from the University of Minnesota advises consumers consider the variables before clicking buy.

The Associate Director of Genetic Counseling said the kits aren’t always accurate. She explained how people have roughly 3 billion letters in their genomes, and the kits test roughly 1 million of them.

READ MORE: As Domestic Violence Is On The Rise In St. Paul, A New Program Is Offering Free Consultations

“And so, of those million, they do a really good job at detecting them, so 99.9 percent accurate, but that still leaves about 1,000 of those letters that can be incorrect,” said Zierhut. “So if they are incorrect in an area that’s really important, that can have serious implications.”

The tests can also connect family members who didn’t know each other existed. She says that is much more reliable, as it matches the percentage of shared DNA.

All of the companies say they do not share the DNA data they collect, unless the consumers give them permission, which is an opt-in feature often labeled under “research purposes.”

READ MORE: Plymouth Police Search For Vehicle In Hit-And-Run Of Bicyclist

“And it’s not totally known how that information will be used,” said Zierhut. “Some people want to give that information for altruistic purposes, to really try to move these big questions forward, and other people really just do it for fun.”

She also says consumers who plan to give a DNA kit as a gift should understand the differences between each company, as the information users receive can vary.

“If you’re looking to have fun and have really cool graphics, you might look for 23 and Me. If you’re looking to connect with relatives and dig deep into your history and public records, you’re going to look at Ancestry. Or if you want to connect yourself to kings and queens and various different people throughout history, then you might [choose] National Geographic,” said Zierhut.

MORE NEWS: 'Extremely Concerning': Wisconsin Farm Where Chronic Wasting Disease Was Detected Sent Deer To Minnesota

The kits usually cost $60 to $100 or more, depending on the information it collects.