What is an autosomal DNA test?

Written by Ellen Hinkley
16 December 2016

To answer this question, let’s start with a little science… Human beings inherit 23 chromosomes from each parent and these sit together in the nucleus of your cells as 23 pairs. One pair are known as your sex chromosomes and they determine your biological gender (X & Y for male, X & X for female), the other 22 pairs are known as autosomes. Autosomal DNA testing is the method by which you can trace your ancestry by having your autosomes analysed.

Autosomal DNA testing is popular because it can report on your combined ancestry from both parents, this is because approximately 50% of your autosomal DNA is inherited from each parent (it’s not exactly 50% because chromosomes can break down and recombine when you’re conceived). As it’s not possible to determine which autosomes or autosomal segments you’ve inherited from which parent; autosomal DNA testing can only be used to trace ancestry that isn’t specifically maternal or paternal.

If you’d like to learn more about the types of autosomal DNA test that are on offer, you can visit our genetic ancestry testing page, click the ‘Compare Tests’ button next to the genetic ancestry testing companies we’ve listed, and check out the ‘Autosomal Analysis’ or ‘Autosomal Analysis & Family Finder’ tests.

What can an autosomal DNA test tell me?

Autosomal DNA tests can identify the population groups (e.g. Celtic, Western European, Scandinavian) with whom you share a proportion of your autosomal DNA, thereby revealing your DNA heritage. The results can then be used to produce your ethnic profile (aka your ethnic breakdown), and by comparing this profile to the typical profiles found in individuals in modern countries; the general location of your ancestors during the thousand year period before the era of mass migration (circa 1850) can be inferred. Autosomal DNA tests that focus solely on revealing your ethnicity are sometimes known as ethnicity DNA tests.

It’s important to note that as the number of our ancestors increases exponentially the further back we go (we each had 32 ancestors five generations ago, each being responsible for just over 3% of our autosomal DNA), many geneticists believe that trying to learn anything meaningful about even earlier generations from our autosomal DNA is not possible.

Hominin ancestry
Autosomal DNA tests can also reveal how much hominin DNA you possess – hominins include Neanderthals and Denisovans, and these ‘cousin species’ are thought to have bred with our human ancestors before they died out around 50,000 years ago. As a result, between one and five percent of the DNA possessed by modern Europeans has been inherited from hominins.

Family Finder
Many of the genetic ancestry companies that offer autosomal DNA testing (e.g. 23andMe, Ancestry.com, Family Tree DNA) will give you access to their customer database once the test is complete. This ‘Family Finder’ feature will allow you to identify any living relatives (aka ‘matches’) who may also have taken a test with that company. This is sometimes known as DNA genealogy.

Most companies will automatically display your matches after you log in to get your results, and show them in order of relatedness. Some will allow you to search for individuals according to the information in their profiles (e.g. their surname) so that you can determine your level of relatedness to that person.

One of the main methods used by these companies to identify matches is by comparing a given region of your DNA with the same region for others on the database. The difference between a given region for any two individuals is defined as ‘genetic distance’, and the volume of DNA shared by those individuals in that region is measured in centiMorgans (cM). If genetic distance is sufficiently low (the individuals share more than 5-7 cM of DNA), they are considered to be closely related.

Another method used to determine matches is by calculating the number of Single Nucleotide Polymorphisms (SNPs) that you share with others on the database. If you share more than 500-700 SNPs with an individual, this person would also be considered one of your close relatives.

Some companies will allow you to search their database for matches according to the number of shared cM or SNPs that you specify. If you set a high number of cM or SNPs, you’ll receive few matches with a high degree of relatedness (e.g. dozens of 2nd to 4th cousins). If you set a low number, you’ll receive many matches at all degrees of relatedness (e.g. hundreds of 2nd to 8th cousins).

For each match you find you’ll usually be able to identify the number of cM or SNPs that you share with that person. You’ll also be able to view their profile which may contain their family tree, ethnic mix and country of residence. In most cases, you’ll be able to contact your matches to discuss your shared ancestry, but in some cases, they may not wish to be contacted and may have disabled this feature.

It’s worth remembering that not all genetic ancestry companies will give you access to their customer database after you take their test. If finding living relatives is important to you, make sure you check for this feature before purchasing, and consider taking a test with each of the major companies (e.g. 23andMe, Ancestry.com, Family Tree DNA) to improve your chances of finding a match.

How does autosomal DNA testing work?

Autosomal DNA testing is usually performed by analysing the genetic variants (aka SNPs) that are present in our autosomal DNA. SNPs arise naturally over time and although some can have detrimental effects, most are harmless. As SNPs are passed down from generation to generation within certain groups, they can be used to identify when one group of humans separated into two distinct populations (one with a particular SNP and one without). By cross-referencing these SNPs with those found in both archaeological remains and modern populations; the population groups with whom you share your SNPs can be identified.

Generally, when you return a cheek swab or saliva sample to a genetic ancestry company, they’ll put your DNA in solution and run it across specialised computer chips. These chips are usually configured to seek between 600,000 and 1,000,000 SNPs in your autosomal DNA, and around 100,000 SNPs will be identified once the process is complete. Although it is estimated that we each possess 10,000,000 SNPs, many of these have not yet been linked to population groups and so are not accounted for when producing your ethnic profile.

A less common type of autosomal DNA testing is conducted by looking for Short Tandem Repeats (STRs), which are repeating sequences of nucleotides e.g. ATCATCATC. STRs also arise naturally and are mostly harmless, but they’re better for confirming a relationship between two immediate family members (e.g. parents, siblings).

Combining genetic ancestry with traditional genealogy

Some genetic ancestry testing companies offer a ‘family tree builder’, so that you can recreate your family tree within their interface and more easily link your matches to your tree. It can be fairly straightforward to link your matches to your tree if those relatives have been identified according to Y DNA tests or mitochondrial DNA tests, however, as discussed above, matches identified according to your autosomal DNA cannot be matched to either your paternal or maternal lineages. Therefore, it may take a little more research before you can add an autosomal match to your family tree.

Uploading and downloading digitised DNA data

Many autosomal DNA testing companies allow you to upload your digitised DNA data to their platform for results, instead of requiring you to provide a biological sample (providing that the data has been produced by one of the main genetic ancestry testing companies). The price of analysing digitised DNA data is often lower than the price of a full test, and some companies even offer this analysis free of charge!

Similarly, many companies allow you to download a digital copy of your DNA data once you’ve taken their test, in order to extend the use of their service. The download will usually take the form of a text file and will be 10 to 30 MB.

You may be wondering ‘Why would I want my autosomal DNA to be analysed a second time?’ One reason is that autosomal DNA testing companies will use different reference populations to produce your ethnic profile, so your profile will vary depending on the company you buy your test from. Similarities or variations across your ethnic profiles may confirm or call into question the ethnicity of your recent ancestors.

Another reason for having your autosomal DNA reanalysed is that if you’re looking for living relatives, you’re more likely to find matches by searching all the major databases, instead of just the database owned by the company you’ve taken your test with.

How much does autosomal DNA testing cost?

Autosomal DNA tests range from £60 to £200 but the most popular tests are between £80 and £150. Some tests will only analyse your autosomal DNA while others will include a Y DNA and/or mitochondrial DNA analysis too. If you haven’t bought a genetic ancestry test before, we’d recommend you buy a test that analyses all three types of DNA at the same time. People often purchase a Y DNA test and mitochondrial DNA test after reviewing their autosomal DNA test results, and it’s much cheaper to buy the three analyses as a package!

If you’re interested in buying an autosomal DNA test but money is tight, the major companies often offer holiday discounts, especially on the run-up to Christmas, so keep an eye out!

What’s contained in an autosomal DNA testing kit?

After you’ve ordered your autosomal DNA test, you’ll receive a kit in the post that contains the equipment required to provide a sample (samples are normally collected using a painless cheek swab or a saliva collection tube). The kit may also contain online registration instructions, a consent form, an envelope for returning the sample, and a booklet that explains what you can expect from your results.

Before you return your sample, you’ll normally be asked to register online so that your sample can be linked to your online account. Once this process is complete and you’ve returned your sample, you’ll have to wait two to 12 weeks before the results are uploaded to your account. Most companies will email you when the results have been uploaded, but some will simply expect you to check your account for the results after the stated ‘processing period’ has elapsed.

You’ll be pleased to know that many genetic ancestry companies will update your results free of charge as new research is published, or if new individuals have been identified as matches.

How is an autosomal DNA test different to a Y DNA test or a mitochondrial DNA test?

Autosomal DNA tests are one of three main types of genetic ancestry test. There are also Y DNA tests to help you trace your paternal lineage and mitochondrial DNA tests to help you trace your maternal lineage.

Although both men and women can take mitochondrial DNA tests (because we all possess mitochondria in our cells), women are unable to take Y DNA tests as they do not possess a Y chromosome. However, if you’re female and you’d like to learn more about your paternal lineage, you can ask a close male relative to take a Y DNA test on your behalf – read our article about Y DNA testing for more information.

Paternal and maternal tests can also be used to help you find living relatives, providing the company you purchase the test from offers a Family Finder feature.