What Is Autosomal DNA Testing? [Best For Family Trees, Ethnicity]

November 11, 2019 by MadAboutGenealogy

The autosomal DNA test is the most widely used DNA test type. It takes into account more than 95% of all DNA we possess. The autosomal DNA testing is pretty much the basis of every single DNA test as it serves as a genetic tracker throughout centuries of time.

It is based on analyzing our autosomal chromosomes (largest chunk of our DNA). All we have to do it provide a saliva sample.

What are autosomal chromosomes anyway?

Well, our whole DNA consists of 22 chromosomes (packets of genes) and our sex chromosomes (XY for men and XX for women). In autosomal DNA testing, we analyze 22 out of 23 chromosomes and even add the analysis of the X chromosome (that is the X chromosome provided by our mothers).

What questions can autosomal DNA analysis answer? 

Analysis of autosomal chromosomes is perfect for 2 things:

  1. Finding out who you share a common ancestor with. Perfect for building family trees (1st, 2nd, 3rd cousins) and figuring out if ‘that twice removed Sophie your mom used to talk about is related to you in any way’.
  2. Determining where your ancestors came from (also known as biogeographical ancestry analysis). Are you 5% Irish or 10% Italian? How much German DNA is in you? And so on.

The autosomal DNA test is the most important of all DNA tests.

That’s why we’ll go through some very interesting questions (and misgivings) are autosomal testing (and we’ll even share the best autosomal DNA tests in the end) that include:

  • What is autosomal DNA (atDNA) and from whom do we get it?
  • How many generations does atDNA go back?
  • What can autosomal DNA tell you about your ethnicity?
  • Which autosomal DNA test is the best (for family trees and biogeographical analysis)?

Understanding how autosomal testing works will make you value the results of DNA tests much more.

Table of Contents

  • What Is Autosomal DNA?
    • From Whom Do We Get Autosomal Chromosomes?
      • How Many Generations Does Autosomal DNA Go Back?
      • Is Autosomal DNA Testing Accurate?
  • Which Autosomal DNA Test Is The Best?
    • Best Autosomal DNA For Family Trees
    • Best Autosomal DNA Test For Ethnicity

What Is Autosomal DNA?

Autosomal DNA is such a large part of our genome that we might as well call it just “DNA”. In shorts, it’s an incredibly big chunk of our DNA.

Our DNA consists of 23 packets of genes – these we call chromosomes – and the first 22 packets of genes we call 22 autosomal chromosomes.

To complete our whole genome we only need to add sex chromosomes – XX chromosome for women and XY chromosome for men.

In fact, the word ‘autosome’ comes from Ancient Greek: ‘auto’ means ‘oneself’ and ‘soma’ means ‘body’. That means that auto-somal DNA literally means ‘oneself’s body’ or ‘our own body’ because the autosomal DNA encompasses such a big part of our whole DNA.

Chromosomes 1-22 are actually numbered, and they contain a varied number of genes. For example, Chromosome 1 is the biggest chromosome. It has 1,961 genes and represents 8% of all DNA we possess. Chromosome 21, on the other hand, is with 215 genes the smallest chromosome and represents 1.5% of our genome.

For comparison, the X chromosome has 804 genes and the Y chromosome has only 63 genes.

Note: Autosomal DNA tests take into account 22 autosomal chromosomes + X chromosome that we all get from our mothers.

From Whom Do We Get Autosomal Chromosomes?

Autosomal DNA serves as a genetic tracker throughout centuries of time. That is only possible because of the following principle:

We get one set of chromosomes from each parent. That’s why half of our autosomal DNA is from our mother and the other half is from our father.

All DNA tests look at specific genetic markers (known as Single-Nucleotide Polymorphisms or SNPs for short). These markers are used to match our DNA with the DNA of our ancestors.

Our recent ancestors – mother and father – each give us 1/2 of their specific markers. Your mother, again, got 1/2 of their SNPs (DNA markers) from your grandmother and grandmother.

Effectively, you have:

  • 1/2 of markers from your mother.
  • 1/2 of markers from your father.
  • 1/4 from your grandmother.
  • 1/4 from your grandfather.
  • 1/8 from your grandmother’s mother.
  • 1/8 from your grandmother’s father.
  • …. and so on.

In general, the number of specific DNA markers you have is reduced by 50% every generation back you go. The further back you go, the fewer SNPs from that person you will have in common.

How Many Generations Does Autosomal DNA Go Back?

As you can see, the share of autosomal DNA markers is cut in half with every generation. In fact, autosomal DNA tests can accurately predict your ethnicity background going back 6-10 generations.

After the 10th generation, the DNA data is not sufficient enough to make an accurate enough estimation about your ethnic background.

Y-DNA tests (following the paternal line) and mitochondrial DNA tests (following the maternal line) can delve much deeper into your past. Those cases uncover ancestors that walked around Europe and Africa well over 1,000 years ago.

The oldest generation of autosomal DNA can uncover (with sensible accuracy) is usually the 8th generation. This serves as useful information for everybody who is trying to put together their genealogical family tree with European, African or Native American ancestry.

For example, if you had a greatgreatgreatgreatgreatgreatgreatgrandfather (7x great) that is that lived in 18th century in Europe (Ireland, Italy, Germany and so on), you can find out how much of DNA (in terms of SNP markers) does he share with you.

Here’s how this calculation goes: The 18th-century European ancestor is 8 generations before you. Because the SNPs are reduced by 1/2 every generation, we simply calculate: (1/2) to the power of 8.

This gives us the result: 1/256. This means that our European ancestor from 18th Century shares with us 1/256 SNP markers. That’s much less than 1% of autosomal DNA.

The 10th generation ancestor, for example, shares less than 1/1000 of autosomal DNA with us. Such a small amount is usually not sufficient to make a match with any degree of accuracy.

Is Autosomal DNA Testing Accurate?

In short, autosomal DNA tests are accurate. However, accuracy depends on how many generations back you want to go.

Nonetheless, the autosomal DNA testing is most frequently (and reasonably) used to pinpoint our 2nd generation ancestors (grandparents and other second cousins). This is to ensure the accuracy of the DNA testing results.

Every generation deeper we go reduced the accuracy of the autosomal DNA testing. We might be tempted to check out our greatgreatgreatgreatgreat grandfather with autosomal DNA testing. However, it does make much more sense to use Y-DNA testing instead.

The problem, of course, if that the guys with the biggest database – Ancestry.com – primarily provide autosomal DNA testing. For Y-DNA testing, we have to check out with the genealogists that are best at determining where your ancestors have originated from – 23andme.

Which Autosomal DNA Test Is The Best?

With pretty much every DNA testing company out there offering autosomal DNA testing, it’s important to make the right choice when choosing the best autosomal DNA test.

What is important to remember is that every company is somewhat specialized for specific types of DNA tests and specific purposes. What does that mean in practice?

You have to decide what you want to know. Usually, people are using autosomal testing to answer one of these two questions:

  1. “Who am I related to?” These tests help you build your family tree.
  2. “What is my ethnicity? Where do my ancestors come from?” These tests do biogeological analysis and you get those nice pie charts that tell you you’re 5% Italian, 3% Irish and so on.

Best Autosomal DNA For Family Trees

Ancestry.com is specialized for genealogy and building family trees. Their autosomal DNA test is the best for answering “Who am I related to?” simply because they have the biggest database of people who took their test.

That means that when you take their autosomal DNA test, they will have millions and millions of people who could potentially be your relatives. In fact, they have 20 million people they can connect you with the autosomal DNA test.

Other DNA tests are not less accurate or anything; they simply don’t have such a large database of people that they could match you to.

Best Autosomal DNA Test For Ethnicity

If you want to find out your ethnicity, you should be looking for the autosomal DNA test that can pinpoint the largest number of regions your potential ancestors came from.

Translation: the best ethnicity autosomal DNA test should have the largest number of regions.

Here’s the difference between a bad and good ethnicity DNA test and what they tell you:

Bad ethnicity test: You’re 10% Central European.

Good ethnicity test: You’re 2% Italian, 5% German, 1% Swiss and 2% Austrian.

Best ethnicity test: You are 1% North Italian, 1% Italian from Milano, 0.5% German from Bremen, 0.3% German from Bavaria … and so on.

The basic principle is that the best ethnicity DNA test will truly pinpoint the location your ancestors came from down to not only a continent (Europe) or a country (Germany) but down to an individual province (Bavaria) or even a city (Bremen, Berlin, Hamburg, Cologne, etc.).

The 23andme.com ethnicity test is the best not because it’s that much more accurate or of high quality. It’s simply because they have the largest amount of regions – they now have 1000+ regions – that your ancestors could have come from.