Before taking that DNA test: Six things you need to know

Updated: shared a statement about privacy. See below.

When you get a DNA test kit, you’ll get a set of instructions to follow so you can get a sample of DNA from your body to the lab. You’ll either be asked to spit into a tube or wipe a swab around inside your mouth.


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Some folks have difficulty producing enough saliva to do a spit test. If you often have a dry mouth, you might want to consider one of the cheek swab tests. Another trick is to think about lemons, the taste of a lemon, and biting into a lemon. Sometimes just the thought will increase mouth saliva.

Also: My ancestry adventure: When DNA testing delivers unexpected and unsettling results

Saliva. Not your usual ZDNet topic. So, rather than imagine the bitter taste of lemons in your mouth as your face crinkles up slightly from the tart taste and you feel your mouth water, let’s talk about some important things you need to know.

1. Know what DNA testing involves

DNA can tell you a lot about yourself. Imagine you’re reverse engineering source code for a video game. If you find a function that solves a puzzle, you can intuit that the game includes puzzle solving. If you find a function in that code for jumping and climbing, the game might have more action elements.

DNA tests can do this, by looking at your DNA to determine what “functions” it exposes in your genetic code. That’s why some DNA tests are able to provide health and lifestyle information.

Also: Soon, your brain will be connected to a computer. Can we stop hackers breaking in?

With the permission of their customers, many DNA companies store DNA data from thousands or millions of customers. By matching your DNA against the DNA patterns of all those other DNA test participants, some DNA companies are able to tell if you share unique sequences, essentially proving that you share ancestors somewhere in your family history.

That opens up one of the biggest services offered by DNA testing providers: Helping you understand your family tree, the migration patterns of your ancestors, and even identify relatives you never knew you had.

2. Be aware there is a dark side to DNA testing

This also opens up one of the more disturbing aspect of DNA testing: The privacy implications. Your DNA is, fundamentally, the source code to… you. If DNA companies are sharing that code, whether with law enforcement or with other companies, it can be a little unsettling. If you authorized that sharing, it’s one thing.

But if your family member or cousin authorized sharing their DNA, they have also, essentially, allowed a considerable amount of your DNA to be shared. And that doesn’t even include what happens if your testing service provider gets hacked.

Also: Genealogy sites credited with helping ID Golden State Killer CNET

The other issue is for those folks who took DNA tests and got back results they didn’t expect. There are many issues involved with this, from what’s called “misattributed paternity” to issues of race, what you’ve been told as part of your family history, and disturbing discoveries about your family tree. When I tested three DNA services, I got some disturbing results.

Keep these unexpected consequences in mind if you decide to move forward doing DNA testing.

3. Know how to choose a DNA testing service

To help you navigate through the offerings of various DNA testing services, we recently produced a guide for CNET. In it, we looked at how well these providers can help you learn about yourself through DNA. Each provider is shown with the size of its matching database. If you’re looking for family information, the bigger the database, the better the chance you’ll find long-lost family members.

Also: Genealogy database used to identify suspect in 1987 homicide CNET

When it comes to health and lifestyle information, the DNA tests use some of the same information. This is really a matching process, but instead of looking for family members, the test provider looks for matching characteristics, particularly genetic markers for certain diseases and traits.

4. Understand the structure of DNA

DNA, is essentially, code. The order and combination of the code provide instructions for creating organic material.

Segments of DNA convert amino acids into proteins. Proteins do all sorts of things, including create new cells. That’s how you get the building blocks, from amino acids to proteins, proteins to cells, cells to tissues, tissues to organs, and organs to people, dogs, trees, cats, and so on.

Also: The startling future of DNA genome editing TechRepublic

Long strands of DNA are called chromosomes. These chromosomes are passed from both a father and a mother to a child. The child’s DNA contains code that represents characteristics of both parents.

5. Know the limits of DNA matching

These chromosomes not only contain code for genetic characteristics, they also contain something of a genetic fingerprint of the parents in each child. That’s why two siblings, born of the same two parents, will share a considerable amount of chromosomal data.

Cousins, too, share chromosomal data, just not as much. The fingerprint has, essentially, been diluted. As you move back in time to grandparents and great grandparents and great great grandparents, and then down other branches of the tree to first cousins, second cousins, third cousins, fourth cousins, and so forth, less and less of the DNA sequences will match.

The reason you need to understand a bit about chromosomes is that you’re about to make a decision: Which test type do you choose? That’s next.

6. Understand the test types

Generally, there are three different test types: Autosomal, Y-DNA, and mtDNA.

Today, autosomal tests are the most common. They can be administered to both men and women, and trace back through the lineage of both sexes.

The Y-DNA test can only be administered to men, and traces DNA back through the patrilineal ancestry (basically from father to grandfather to great grandfather).

The mtDNA is matrilineal and lets you trace your ancestry back through your mother, her mother, and her mother going back.

Autosomal tests can get you quality genetic information going back about four or five generations. Because the Y-DNA and mtDNA tests are more focused on one side of the line, you can get information going back farther, but with less data about family structure.

Which test you take depends entirely on what you’re looking for. Don’t expect perfect accuracy. They can give you indications, but taking a DNA test won’t magically produce a history book of your family’s background.

My experience

So, there you go. In the guide, we present to you 10 of the more interesting DNA services we’ve found. Some are better than others, so you should not only take our information into account when spending on a service, but look for reviews and stories posted by those who have used the services to see what their experiences have been.

I, personally, have now tested three services: Ancestry, 23andMe and LivingDNA. It’s been interesting — and also disturbing. By combining the DNA tests with Ancestry’s research database, my wife and I were able to answer some long-kept mysteries about our family trees. Here’s my story about that, as well as in-depth reviews of those three services:

Also: My ancestry adventure: When DNA testing delivers unexpected and unsettling results

By the way, a spokesperson at Ancestry reached out to me to talk about the data privacy concerns I raised in this article. They wanted to share this statement:

Protecting our customers’ privacy is Ancestry’s highest priority, and that starts with the basic belief that customers should always maintain ownership and control over their own data. We will not share customers’ personal information with third-parties – including insurers, employers, health providers or external marketers – without their explicit, informed consent. Ancestry will not share any DNA data with law enforcement unless compelled to by valid legal process and will always seek to minimize the impact on our customers’ expectations of privacy.

I am personally fascinated by Ancestry and the work they’re doing, so I hope to be able to bring you more from them over time.

Stay tuned. If I can, I’ll do more tests and report back to you here on ZDNet and CNET about what I learn.

You can follow my day-to-day project updates on social media. Be sure to follow me on Twitter at @DavidGewirtz, on Facebook at, on Instagram at, and on YouTube at

Previous and related coverage:

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92 million accounts for DNA testing site MyHeritage found online

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