Spit in a little tube, mail it in, and wait for the results. That’s all you have to do when taking a gene test by the companies 23andMe and AncestryDNA. Health information is a major reason for the rapid growth in gene testing. But watch out: When the DNA report comes back, everything you think you know about yourself and your family can change in an instant.

Katy Canning never exactly looked like her parents. “My mom would tell me when I was growing up, ‘Oh, you’re part Native American. You’re Native American,'” she told correspondent Tony Dokoupil.

But when she finally took an at-home DNA test about five years ago, she got a lot more truth than she expected. She’s part Jamaican, for starters, and her biological father is not the man who raised her, but a traveling guitarist named Baron Duncan.

“It is crazy, so crazy,” Canning said.

And the revelations kept coming, as Canning learned that Baron Duncan had at least four other children, her half-siblings. 

“You grew up thinking that you were the oldest of two, and in fact you are the oldest of five?” asked Dokoupil.

“Exactly.”

“Do they look like you?”

“So much!” Canning said. “Meeting my brother Stephen for the first time, it was like looking at my twin. I literally started crying as soon as I saw him.”

Canning is one of millions who have turned to home DNA tests, and one of many who have had their sense of identity shaken by the results.

23andMe and AncestryDNA both warn customers they could receive shocking information, but neither company offers genetic counseling as part of their standard package.

“People are smart enough and capable, they can make sense of it,” said Emily Drabant Conley, vice president of business development at 23andMe. She believes customers can handle genetic information, just as they do the results of other at-home exams.

“People take a pregnancy test at home and if it’s positive, which is significant information, they then take the next step of talking to a doctor, and we think that DNA tests are very much in the same vein,” Conley said.

AncestryDNA says it takes “the potential impact of complex discoveries … very seriously,” and has a team available for people with “more sensitive queries.”

But DNA tests also raise questions about privacy.

23andMe says it won’t share customer medical data with third parties unless given explicit consent. The company also says it uses two-factor authentication and encryption to protect genetic results, and has never been hacked.

But privacy expert Peter Swire says just one breach would be hard to fix. “If you have your credit card stolen, you cancel it and get a new credit card in two days,” he said. “If your DNA gets revealed to the world or to the hacker, it’s really hard to get new DNA. It just doesn’t happen.”

Dokoupil took a test himself, and braced for a surprise (“I am an only child of unmarried parents who lived a wild and crazy hippie existence…”) that never came. “Twenty-six-point-six percent Italian, as expected with a first name like Tony,” he said.

Canning, though, is still working through the meaning of her own results, knowing she is now Jamaican-American: “That is the weird thing – am I allowed to say that? I don’t know. Can a DNA test tell me what I am and what my identity is? I don’t know.”

Canning told us her biological dad died before she could meet him, but her mother did come clean about him in the end (explaining, “It was the ’80s”). But she’s sure of one thing: her father is her father.

“He doesn’t care what a DNA test says; I’ve been his since the moment I was born,” she said. “Family isn’t just blood, but family is what you make it, and family is your heart, and my dad is my dad. He will walk me down the aisle one day.”