What Really Happens to Your DNA Sample After You Swab?

By: Jim Brewster

Have you ever wondered what happens to your DNA sample after you send it in for testing? We take you through the lab process behind DNA testing to give you a better understanding of what happens to your sample and how it’s analyzed. From sample collection to data interpretation, we’ll walk you through each step of the process to demystify the world of DNA testing.

Congratulations! As a proud new tester, your sample enters this world weighing almost nothing. What challenges will this fragile new sample encounter as it learns and grows and struggles to find its place in this big, wide database? I’ll be your host, David Attenborough Jim Brewster as we explore the world of the DNA sample. [cue epic inspirational music]

What Is a Sample?

Before we start looking at what happens to the sample, let’s take a moment to explore what the sample is in the first place. This may seem like an obvious question, but there is a lot more than DNA that goes into a test vial when you swab your cheek. When you scrape the inside of your cheek, you get cheek cells, saliva, bacteria, the blueberry muffin you had for breakfast, your hopes and dreams for the day, etc. All of this is collectively referred to by the scientific term “Sample Stuff,” which is totally a real term and not something I made up.

The cheek cell is the important part of this Sample Stuff, as the DNA lies inside. DNA is inside the nucleus and the mitochondria, both of which are surrounded by cytoplasm, organelles, and other five dollar words. These are all protected by a cell membrane. So the golden nuggets of DNA are pretty well protected.

Cheek cells and friends then go into the plastic vial full of liquid. That liquid has several components. First, it has some preservatives that help prevent the bacteria in the swab from growing. It also contains a lysis buffer. Lysis works to burst the cell membrane so we can get at the DNA goodness inside.

The Lab Journey

After swabbing and signing the necessary paperwork (I mean, where would we be without paperwork?) the sample makes its way to our lab in Houston, Texas, USA.

Receiving the Sample

First, it is received by our accessioning team, who scan the paperwork and the sample barcodes and send one vial to the lab to be processed and the other vial to storage for future use. The lysis buffer helps preserve the storage sample, so it can remain viable for years at room temperature for future testing.

Entering the Lab

The first step in the lab is to mechanically extract the Sample Stuff from the vial. Next, a chemical called Proteinase K is added. Proteinase K helps break down the proteins inside the cell so that the DNA can be separated from the other Sample Stuff.

Some of these proteins (such as histones) protect the DNA from degradation, so from this point on, the sample must be kept in cold storage to prevent decay. Our state-of-the-art sample freezer keeps the extracted samples at -20 degrees Fahrenheit at all times. We also have a backup generator so the samples can be maintained in the event of power outages.

At this point, the rest of the steps in the testing process will probably make more sense if we first discuss the chemical structure of DNA, since this structure is what ultimately provides the information the lab needs to unlock.

A Short Interlude About DNA Structure

Most people know the famous double helix shape of DNA first published in 1953 by Watson and Crick. This shape, discovered by Rosalind Franklin, is composed of two strands of phosphate polymers that form two spiral strands, wrapping around each other. These strands are connected like rungs on a ladder, and there are many components within this shape.

You may think of plastic when you think of a polymer, but a polymer is just a group of large molecules made of many repeating subunits. Think crystals, hair, that gross jello stuff with hotdogs in it that was popular in the 70s, the sickly green upholstery that was also popular in the 70s… Honestly, the 1970s were a dark time for polymers. Not that the 80s were doing well either, what with the neon windbreakers. Anyway, I digress.

In the case of DNA, the polymer is a chain of phosphates that form two spiraled strands. These strands are connected to each other like rungs on a ladder by four chemicals called nucleotides, abbreviated as A, C, T, and G. These stand for adenine, cytosine, thymine, and guanine. Each rung is composed of a nucleotide pair, with one half on each strand. We call this a base pair.

Because of their chemical structure, in each base pair, A is always paired with T, and C is always paired with G. This means if we look at a specific position and see an A on one strand, we know there is a T on its companion strand. This is referred to as “Chargaff’s Rule” after the Ukrainian geneticist who first identified this phenomenon.

There are millions and millions of base pairs in our DNA. Through hard work, geneticists were able to map out this “ladder” in a method much like putting together pieces of a very complicated puzzle. Each base pair is assigned a position, like coordinates on a map, to find where it fits in the puzzle.

Ok, back to the lab.

Testing Your DNA

Now that we have extracted DNA from the other Sample Stuff, we can run tests on it. We want to make sure that we only use a portion of the sample in case we need to rerun a test for accuracy or run additional tests in the future.

The meat and potatoes of DNA are the nucleotide pairs. Those are the pieces of information that can vary from one person to another and that unlock the history of our ancestry. The next step, then, is to peel apart the strands to see the nucleotides within. We do this with an enzyme called helicase, which is naturally occurring.

Remember Chargaff’s Rule? When a DNA strand is peeled apart, copies of a complete double helix can be made from a single strand because only the A on one strand will always bind to T and G to C. New polymer chains are built, and they are connected to the two half strands with complementary nucleotides at each base. Essentially, a mirror image of each strand is made, and one helix becomes two. This is how cells grow and divide naturally.

We can do the same thing artificially. We can make more and more copies using a process called a polymerase chain reaction, or PCR. With PCR, we can make millions of artificial copies of your DNA. These artificial copies are limited in their shelf life, but they allow us to do two important things.

First, having many copies ensures that we can get reliable, quality reads on more regions of your DNA. Second, we can take only a small portion of the extracted sample while leaving the rest in cold storage for future testing.

Now that we have millions of copies of your DNA to study, how do we actually study it? How do we find out what nucleotides are attached to the strands? Contrary to popular belief, we do not actually have hundreds of teeny tiny gnomes with magnifying glasses to look at your DNA. I know, I was pretty sad to find that out, too. Talk about disillusionment.

Instead, we use a property of chemicals called fluorescence spectroscopy. I know, it’s a mouthful, but bear with me.

Fluorescence Spectroscopy

Different chemicals and elements react differently and at different wavelengths when subjected to radiation such as light or heat. This is called fluorescence. A white fluorescent light, for example, is a tube of mercury vapor. Mercury vapor fluoresces white when you introduce a low-level electric current, and this is what causes the bright white shine. All the different colors of neon lights work the same way.

When we use the PCR process to create extra copies of your DNA, we also add special chemicals that make the artificial nucleotides fluoresce as well. Different test types (Y-DNA, Family Finder, mtDNA, etc.) are run on different machines using different processes, but each utilizes this principle to read the nucleotides. The strands are aligned and run under lasers that are attuned such that each nucleotide will fluoresce at a different wavelength.

This process is repeated several times so that even if some of the copies had a slight copy error or if the laser had a slight misread, we could make sure the results were reliable.

Analyzing the Data

Now we have a massive amount of data, with different wavelengths read at different locations. All of this data is then sent to our analysts for review.

The initial process is designed to detect any abnormalities in the testing process and to make sure that the results that were produced are within the parameters of what we would expect to see. Abnormalities are flagged for closer scrutiny, and if needed, the samples are rerun.

Transcribing Your DNA

Next, the data is processed into a readable format. The results for each test require specialized software, so the data is sent to the appropriate section of the network. We feed it into the appropriate proprietary software, which translates this data into results.

For example, the autosomal DNA is compared against our reference populations in our myOrigins database to provide your regional breakdown of ancestry.

The results then undergo a final quality control check and are uploaded to the database.

The End Result

And there we have it, folks. From cheek swab to computer, the trials and tribulations of your sample are over. Now the real work begins as you get to compare this data to your matches and your genealogical records to uncover clues about your family history.

We will keep the remaining extracted sample safe in our cold storage and the second vial in our temperature controlled storage facility. That way, if you ever decide you want to order additional testing, we will have plenty of Sample Stuff to run the test(s) on!

About the Author

Jim Brewster

Contractor for FamilyTreeDNA

Jim Brewster was born at a very early age and gradually became older. He has been in the genetic genealogy field since 2014 and delivered numerous presentations at genealogy conferences. He has helped with collaborations between FamilyTreeDNA and non-profit organizations and for some reason FamilyTreeDNA decided to let him write stuff too.

With a proven track record of both doing things and accomplishing stuff, Jim enjoys presenting and writing about genetic genealogy methods and the science of DNA testing. In his free time, he enjoys puns and cat pictures.