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July 29, 2019
DNA Hack
Is DNA testing for ancestry accurate?
Ancestry DNA tests are only as accurate as the company you choose to test with, because each company uses their own reference populations.
By
Tomohiro Takano

TL;DR

Ancestry DNA tests are only as accurate as the company you choose to test with, because each company uses their own reference populations. (So really research the testing companies before making a choice!) Of course, the accuracy will improve as they collect more region-specific DNA data sets for the reference population, and have more DNA data sets within their database to compare with. Good news for everyone -- the results will get more and more accurate over time without any extra action or effort on your part!

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DNA testing kits are all the rage these days, offering genetic information about family history, health risks, customized dietary suggestions, and even skincare regimens! But how do these tests work? How much can your saliva really tell you about your ethnicity? Can ancestry testing really help you understand your heritage?

Here, we will break down how genetic testing companies evaluate DNA data to determine ethnicity estimates and whether these estimates can accurately trace human history. Let’s begin by looking at the different ways these companies analyze genetic data.


How do DNA tests actually work?

To start with some biology basics, the human genome is a lot like a really, really, REALLY long story. Instead of being written with standard words using the traditional 26-letter alphabet, it is written with a 4-letter alphabet. These four different letters are actually variations of a chemical molecule that are called bases, and our genome contains about 3 billion (with a B)! If bases are like the letters of your genetic story, individual genes can be thought of as paragraphs, and chromosomes can be thought of as chapters. In total, humans have about 20,000 genes located on 23 pairs of chromosomes. Together, these chromosomes contain all of the information needed to build a human being.

So, where does this information come from? In keeping with the book analogy, your whole story is actually like receiving 2 different editions of a 23-chapter instruction manual, one from your mother and one from your father. It may seem silly to buy 2 of the same instructions, but when it comes to DNA it is necessary to have 2 versions that complement each other in case any steps are faulty or incomplete.

Within each set of chromosomes, 1 is a sex chromosome responsible for determining sex characteristics, while 22 are autosomes which provide information for everything else. In humans, there are 2 different types of sex chromosomes; the X chromosome or the Y chromosome. Mothers always pass along one copy of an X, while fathers can pass along either another copy of X to create a female or a copy of Y to create a male.

The average difference between one person’s DNA profile and another’s is about 0.1%, meaning the vast majority of our genetic makeup is the same. However, this small difference accounts for nearly all of the variation we see within humans. Rather than analyzing entire genomes, testing companies skim through the data (“book”) to evaluate regions known to have variations in DNA sequences called single nucleotide polymorphisms (SNPs). These genetic markers are then compared to people from around the world to build ancestry reports, health reports, and even estimate the risk of certain diseases.


In genetic testing, there are 3 primary types of tests used to look at differences in SNP patterns. They are:

  • Autosomal tests- These tests look at the autosomal DNA and do not include the sex chromosomes. Test results can help to identify close family members from either side of the family.
  • Mitochondrial DNA (mtDNA) tests- Mitochondria are present in most cells and contain their own DNA that is passed along from mother to child. It changes extremely slowly so, in ancestry testing, results can provide historical information about the maternal line.
  • Y-chromosome DNA tests- These tests look at genetic data present in Y chromosomes. This version of the sex chromosome is only found in males, so these DNA test results provide information about the paternal line. A woman interested in her Y-chromosome DNA results must collect a saliva sample from a close male relative.

Can these tests accurately determine ancestry?

It all starts by submitting a DNA sample from your saliva. This involves either collecting a sample with a cheek swab or by spitting into a collection container. After just a few weeks, you will receive results that could provide you with DNA matches, identification of a common ancestor, and more!

There are dozens of companies to choose from when looking for DNA testing services to learn about ancestry and family history. Some of the more popular DNA ancestry tests include:

There are a few big things that can affect the accuracy of these test kit results. Check them out below:

  1. Each company uses their own reference populations.

They usually start by analyzing the genomes of people in specific areas that have confident knowledge of their family trees dating back several generations. This gives genealogists an idea of where certain patterns of SNPs tend to exist, though sometimes the information given about a family tree can be incorrect. As genetic testing popularity grows and companies receive more DNA samples, their data sets will expand and become more and more accurate.

  1. DNA services tend to based on regional data, which varies around the world.

There may be certain SNPs that are more common in European populations than in African or Asian populations. If you know you have ancestors from Ireland and the British Isles, completing a DNA kit with a company that has a large European reference population will provide you with more accurate results. On the other hand, if you know you have East Asian ancestors, your results from that same company will probably not be very accurate. Some people have sent their raw data to several companies and received different results from each one.

  1. Genetics are complex.

Although it has been studied for many decades, DNA is not entirely understood. There could be significant SNPs that are not evaluated or recognized as important genetic markers. You also might not inherit certain genes that show your Scandinavian heritage even if your siblings have. Even with the best DNA testing, genes are tricky and cannot tell you everything about your family. Some companies (like Ancestry.com) incorporate the use of historical records to increase their accuracy.


Accuracy of ancestry DNA tests will continue to improve

As more and more people grow curious about their family history and submit their DNA samples, databases will grow and provide more accurate results. Often times they will even reprocess your sample after updating their algorithms to provide you with the most up-to-date information. You can always upload your raw data to other testing sites to have your DNA compared with other reference populations and give you a better idea of your relations throughout the world!


Did you get 23andMe, AncestryDNA, or MyHeritage results back?
Upload your raw DNA data to access 25+ traits for FREE at Genomelink!
Tomohiro Takano
Tomohiro Takano
Co-Founder and CEO
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