How Do DNA Tests Work?

Updated January 26, 2019

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A list of references is also included at the bottom of this article.

Testing your DNA is a simple process, and by completing a test you can learn more about your ancestry, establish paternity, or determine your risk factor for genetic diseases.

What's in this Guide?

Disclaimer: Before You Read

It is important to know that your genes are not your destiny. There are various environmental and genetic factors working together to shape you. No matter your genetic makeup, maintain ideal blood pressure and glucose levels, avoid harmful alcohol intake, exercise regularly, get regular sleep. And for goodness sake, don't smoke.

Genetics is a quickly changing topic.

DNA testing is constantly changing, but here, at YourDNA, we keep up with changes in technology and testing to provide you with the most up-to-date information possible.

Quick Overview

DNA tests are used for several purposes. Sure, law enforcement officers use them to help rule out suspects and ensure criminals are charged for their crimes.

But DNA testing is also used to measure a person’s risk level for developing certain types of cancer, determine who someone’s father is, and to research a person’s family history. It can even be used on dogs to determine their breed and level of health.

In fact, the process has become so common, you can now purchase kits to have your DNA tested without leaving your house. Learn more about DNA, the testing process, and whether DNA testing is something that could benefit you.

DNA testing has become more and more common over the past few years, but many people still don’t fully understand how the process works. The good news is, the process isn’t that hard to understand.

Basically, samples for DNA tests — bodily fluids, skin, and blood are commonly used — are collected and sent to the lab where they are examined for specific genetic markers. The results can help you plan for your future health or help you put together a family tree that goes back generations.

What Is a DNA Test?

Testing involves sequencing your DNA for genetic markers. Your DNA is a part of every cell in your body.

While 99.9 percent of it is identical to others, unless you’re an identical twin, 0.1 percent is unique to you.

So when that small strand of DNA is compared with common genetic markers during testing, the results can be used to prove paternity, research your genetic history, scan for possible genetic birth defects, and determine whether or not you’re predisposed to certain illnesses and diseases.

How DNA Testing Is Done (The Process)

Because DNA is found in all of your cells, extraction is available in multiple forms.

Lab techs can use your saliva, blood, hair, and nails to test your DNA. However, at-home DNA test kits use a cheek swab or saliva collection to keep the process simple.

The part of the process that you experience is easy. All you have to do is submit a sample for testing. This is usually a sample of your saliva or blood.

However, because DNA is in all of your body’s cells, it can be extracted from your hair, nails, teeth, and skin too. But for the most part, saliva or blood samples are used because they are easier to extract the DNA from and have all the markers needed for the testing process.

After you submit your sample, you just wait for your results. If your doctor tested your DNA, you might have your results back in a few days, but if your use an at-home DNA testing kit, you shouldn’t expect to get your results back for several weeks — this depends on the company’s processing time.

DNA Tests with Saliva

When your saliva is used to complete DNA testing, all you have to do is spit in the collection tube. Because your saliva originates from the inner linings of your mouth and white blood cells, it’s easy to extract DNA from them.

Typically, spit is used when it’s needed for forensic purposes, especially in rape or sexual assault cases, because DNA lasts in your saliva for two days.

DNA Tests with a Cheek Swab

DNA tests that use cheek swabs also extract DNA from your saliva. But instead of collecting a saliva sample by spitting in a tube, a cotton swab is used to collect cells from the inside of your cheek.

This type of DNA test is typically used to establish paternity or maternity, to complete an at-home DNA test kit, and for forensic purposes.

DNA Tests with Blood

When your doctor orders a DNA test, there’s a good chance that he or she will complete a blood test instead of using your saliva, nails, or hair. In most cases, this is because DNA testing is ordered with other tests so it’s easier to use test tubes of blood for multiple tests at once.

A blood test can also be used to establish paternity or maternity, and they are commonly used to test paternity during pregnancy. When blood is used to test paternity during pregnancy, the mother’s blood is analyzed — not the baby’s.

A mother’s blood can show signs of fetal DNA as early as seven weeks after conception. However, the amount of fetal DNA seen in the mother’s blood depends on her body weight.

So there’s always a chance that a blood test during pregnancy won’t give you the most accurate results.

DNA Tests with Nails

It’s not common to complete DNA testing using a person’s nails, but it is possible. In most cases, alternative specimens of DNA, such as DNA from your fingernails or toenails, is collected because there isn’t another option.

Because of this, it’s most common to see DNA testing with nails used in forensics or to identify a person’s remains.

DNA Tests with Hair

When DNA is tested through hair follicles, Science has proven that only the shaft of the hair actually contains DNA. This is the part of the hair that hasn’t come out of your scalp yet.

Even then, hair follicles don’t have as many DNA markers as saliva or blood, which makes this type of testing considered a last resort, and it’s mostly used in forensic testing to help place a person at the seen of a crime.

How Do Paternity DNA Tests Work?

Paternity (and maternity) DNA testing uses a process called DNA profiling, which is also known as genetic fingerprinting, to determine the identity of biological parents.

Even though, it’s mostly used to identify parents, this type of DNA test can also determine the likelihood of someone being a biological grandparent to a grandchild.

Paternity tests are completed by comparing two sets of DNA for similar genetic markers. For example, a child’s DNA is compared to that from the person they believe to be their biological mother, father, or grandparent.

To prepare for the test, buccal cells are collected from the inside of each person’s cheek using a cotton swab. The samples are then sent to the lab for testing.

During the testing, the DNA strands are compared to see how many specific genetic markers the two have in common. The results tell you how likely it is that you’re biologically related to the person your DNA is compared with.

While DNA testing isn’t 100 percent accurate 1, paternity tests can confirm a mother or father for a child at an accuracy rate of 99.99 percent. If the suspected parent isn’t related to the child, DNA testing confirms that there is a 0 percent chance of that person being the parent.

Paternity can also be confirmed through DNA testing while a baby is still in the womb. To do this, DNA is extracted from amniotic fluid taken from the placenta using a needle and compared with DNA collected from the suspected father’s cheek swab.

Fetal DNA also shows up in the mother’s blood as early as seven weeks gestation, so if you’re looking for a less-invasive procedure, you can have the baby’s DNA extracted from your blood.

However, it’s important to note that the amount of DNA extracted from the mother’s blood can vary depending on the mother’s weight — so basically testing the amniotic fluid is more accurate. Neither of these tests harms the baby but there are risks associated with any invasive procedure while pregnant.

How Does DNA Testing Work for Ancestry?

DNA testing for ancestry research has become more and more popular, thanks to the availability of at-home DNA test kits.

The process is simple. Once you have a collection kit, you use the included cotton swab to collect a DNA sample from the inside of your cheek or use the saliva collection tube. Then, you seal the sample and send it back to the company for testing.

The lab uses a lineage-based approach to DNA testing that analyzes the DNA on the Y chromosome, which is passed down from fathers to sons or your mitochondrial DNA, which is passed down from mothers to their children.

During the testing process, your DNA is analyzed and run through a database that compares genetic markers with that from the DNA of other individuals on file. As DNA is passed down from generation to generation, slight mutations occur.

These mutations eventually become genetic markers that can be traced back to real people throughout history up until today.

When you use an at-home DNA testing kit, your DNA is added to the company’s database where it’s compared to everyone else who has submitted their DNA. Then, you can look at your results online to see how many people have been found that are related to you and just how closely you’re related.

Because ancestry DNA tests 2 can trace your DNA to find familial matches from the past, you can use these matches to trace how your family migrated from one location to another over time.

How Do Pet DNA Tests Work?

DNA testing isn’t only performed on humans. You can get DNA tests for your pets too.

While it is available for cats and even horses, it’s more commonly completed on dogs because many dog owners are interested in knowing the mixture of breeds in their dog’s DNA. Knowing the specific breed of an animal you own is important because it can tell you if your pet is at a higher risk of developing specific conditions or diseases.

For example, Beagles, Rottweilers, and German Shepherds have a higher chance of getting cancer 3 than some other dog breeds. Depending on the type of test you use, you may also learn whether your pet has any food or medication allergies or intolerances, what type of recessive genes it has, and your pet’s genetic age.

Keep in mind, your pet’s genetic age isn’t the same as his or her chronological age. The genetic age takes the aging of your pet’s cells into consideration, so it can help estimate your pet’s lifespan, but can’t tell you his or her birthdate.

If you’re interested in having a pet DNA test completed, you can either purchase an at-home test kit or have your veterinarian complete the test. At-home kits for animals are really similar to the ones for humans.

They come with a cotton swab and tube, you swab the inside of your pet’s mouth, seal the sample in the test tube, send the tube to the lab, and wait for the results. When a veterinarian performs it, he or she typically collects a blood sample from your pet, which is then sent to the lab where the DNA is extracted and tested.

How Do DNA Tests Find Disease-Related Risks?

In most cases, DNA testing that’s completed to find disease-related risks has to be initiated by your doctor.

The process is still easy, your doctor collects a blood or saliva sample, which is sent to the lab where your DNA is extracted and analyzed. When the tests are complete, your doctor reviews the results to determine which, if any, genetic diseases you have a high risk of obtaining.

However, in 2017, the FDA decided to allow 4 the testing company 23andMe to test for 10 disease types using its at-home kit including late-onset Alzheimer’s disease, Parkinson’s disease, and celiac disease.

When DNA testing is completed by your doctor to find disease-related risks, two processes are used — whole exome sequencing and whole genome sequencing. During the testing process, long strands of DNA are tested to find mutations that occur in your DNA’s exons, which is where most known mutations that cause disease occur.

However, just because you have markers that indicate you might be a higher risk for a certain disease, it doesn’t mean that you’ll actually get it. Lots of people carry the Alzheimer’s disease gene, but they don’t all end up with dementia or Alzheimer’s disease.

When you use an at-home test, like the one offered by 23andMe, shorter pieces of your DNA are examined for genetic mutations, known as single nucleotide polymorphisms (SNPs), that are associated with genetic diseases. This process is faster, but the results are limited.

While DNA testing for diseases can’t determine whether you will or will not end up with a specific disease, it can show you whether you’re at a higher risk. This gives you time to adjust your lifestyle in an effort to prevent the disease.

More importantly, genetic testing like this can tell future parents whether they carry specific genes that increase the risk of their future child having a specific disease.

What Do DNA Test Results Show?

The results of your DNA tests will vary, depending on the type of test you take.

For example, if you take an at-home version for ancestry purposes, your results will show your ethnic background and people in the database who are related to you going back generations.

However, if you have a DNA test to prove paternity, the results will show whether or not the person being tested is the child’s parent. Some of the other things DNA testing can determine include:

  • Risk factors for genetic medical conditions
  • Migration of your family throughout past generations
  • Vital information for your pets such as breed percentages and health factors

Can DNA Tests Be Wrong?

It is possible for DNA tests to be wrong, however, that’s rare.

Typically, when DNA tests are incorrect, it’s because the DNA sample is contaminated or simply because of human error. If for some reason you believe your DNA test isn’t correct, you would need to redo the test with completely new samples.

How Accurate are DNA Test Results On Average?

The results of ancestry DNA tests, DNA tests for medical conditions, and paternity tests are 99.99% accurate on average.

However, it is possible for you to see conflicting results if you have DNA tests completed by multiple companies. This is because each DNA testing company has its own set of traits they test.

So, one at-home kit might tell you that you have the gene needed to have red hair, while another might not mention that. This doesn’t happen because you don’t have that specific gene, it’s just that one company specifically looked for it and the other didn’t.

It also can depend on the amount of information in their database on similar ancestry data.

Pet DNA testing isn’t as accurate if both of your pet's parents are mixed breeds. In cases like these, there often isn’t enough information in the company’s database to test for every breed of animal.

Can DNA Tests Determine Ethnicity?

It’s a common misconception that ancestry DNA tests can tell you your race or ethnicity.

Ancestry tests do show you some of it, but they don’t show everything. DNA is tested through your mother’s mother and her mother or through your paternal line, etc. On top of that, these tests only analyze a small snippet of your DNA.

So if you have DNA testing completed and you discover family members going back 10 generations, you’re only obtaining information for about one out of a thousand or so of your actual ancestors. So basically, while it can give you a general idea, it doesn’t give you the full picture.

How Do DNA Tests Really Work?

These tests analyze a strand of your DNA and compare the specific markers found to other people’s DNA and markers that are normally seen in people with certain genetic conditions.

The process you experience when taking the test is simple — the hard work is all completed at the lab. Once you submit a DNA sample to a lab, the lab techs have to extract your DNA from the sample — your blood, saliva, or skin cells, etc.

After the DNA is extracted, it’s analyzed according to the specific test that was ordered. For example, if you complete an at-home ancestry kit, snippets of your DNA are compared to information already stored in the company’s database to find other people with DNA similar enough that the two of you could be related.

This type of testing can find people in your family dating back several generations. However, if you submit a DNA test to see if you carry specific genes or markers for diseases, such as Alzheimer’s disease or genetic cancer types, your DNA is only tested to look for those specific genes.

Referenced Sources

  1. Paternity Testing
    American Pregnancy Association
  2. What is Genetic Ancestry Testing? 
    National Library of Medicine , U.S Department of Health and Human Services
  3. Estimating canine cancer incidence: findings from a population-based tumour registry in northwestern Italy.
    Elisa Baioni, Eugenio Scanziani, Maria Claudia Vincenti, Mauro Leschiera, Elena Bozzetta, Marzia Pezzolato, Rosanna Desiato, Silvia Bertolini, Cristiana Maurella, and Giuseppe Ru.
  4. FDA allows marketing of first direct-to-consumer tests that provide genetic risk information for certain conditions.
    United States Food and Drug Administration