What Are Autosomal DNA Tests?

Medically Reviewed by Sanjay Ponkshe on February 24, 2024
Written by Alyssa Anderson
5 min read

Autosomal DNA tests are a way of looking at the code that exists inside of all of your cells. They reveal a world of genetic information that can be used medically and to discover your ethnic makeup. These tests have become popular to find relatives and ancestors. 

DNA is a molecule that exists inside the cells of all living things. It contains all the information needed to create life. For example, the DNA in a cat contains all the information needed to make a cat, while the DNA of a human contains all the information to create an individual human. 

The strands of DNA in your cells are tightly wound up into structures called chromosomes. You get 23 chromosomes from each of your parents for a total of 46. Of those, 44 are called autosomes and the other two are sex chromosomes. Autosomal DNA contains most of the code that makes up who you are. 

By reading particular areas of this code, you can find out specific details about your genetic history. You may be able to discover the parts of the world where your ancestors lived, who those ancestors were, or information about your current family relationships and medical history.

DNA is a molecule in the shape of a double helix, which looks like a twisted ladder. The rungs of the ladder are made of smaller molecules called nucleotides. These nucleotides come in four different varieties in DNA: A, G, C, and T. 

Chunks of this ladder form genes, which can be read by special machines in your cells — called enzymes — which turn them into proteins. You’re mostly made of these proteins. 

Mutations —or changes — can appear or be created in these genes. For example, an A could get turned into a C. This change in the code creates a change in the protein. That, in turn, could affect how your body works. The particular order of nucleotides in your genes is called your genotype, while the way these genes affect your body is called your phenotype.  

There are many different services that currently offer DNA tests to find your ancestors and determine your ethnicity. Examples include 23andMe, AncestryDNA, and Family Tree DNA. DNA testing results can include information on who your ancestors are and the amounts of your DNA that come from particular ethnic groups or geographic regions. 

Genealogy tests focus on your ancestors and will combine your genetic information with other sources of data, such as family trees. An ethnicity test will break your chromosomes into sections to determine the approximate ethnicity of each portion of your DNA.

For example, a result that says you’re 32% Irish means that 32% of your DNA matches that of a theoretical 100% Irish person. This is ambiguous, however, because there are many genetic variations even within the Irish population.

Each service handles the testing in slightly different ways, but there are some common elements to all of them. 

The first step to all DNA testing is to take a sample of your DNA. This is typically done through a swab of your cheek cells or saliva. Autosomal testing is done by looking at a subset of regions in your DNA that the companies have determined are helpful for identifying ethnic ancestry.  

Typically, autosomal DNA tests look at less than 1% of your genome — around one million nucleotide sites. You have over three billion of these positions in your DNA.

While they're useful for getting information about both your mother’s and father's lineage, these tests are only accurate about five or six generations back. More autosomal testing on your siblings, cousins, and second cousins can greatly increase the amount of ancestry information that you can get out of these tests. 

Autosomal DNA tests can be helpful for diagnosing particular genetic diseases or predispositions for diseases. A genetic disease involves a particular mutation or sequence in your genetic code. Your doctor will look at small, specific regions of your DNA known to cause or be linked to a certain disease. 

This type of testing includes: 

  • Diagnostic testing. This is used to confirm that you have a particular genetic condition when you’re already showing symptoms. 
  • Presymptomatic testing. This is used when your family has a history of a particular condition and your doctor wants to confirm whether you inherited the causal gene(s).
  • Predictive testing. Certain sequences of DNA are not linked to specific diseases but may suggest that you could develop a disease, like a particular cancer. These tests can tell you if you’re at risk for a certain disease.
  • Carrier testing. Some conditions are recessive autosomal diseases. This means that you need two copies of the mutant version of a gene to have the disease. If you only have one copy you will not have the disease and are called a carrier. It’s good to know if you’re a carrier because you can still pass this gene on to your children. Cystic fibrosis is a fairly common example of an autosomal recessive disease that is caused by a single nucleotide change on one of your autosomes. 
  • Paternity testing. This is a form of genealogy testing that is commonly used in a medical setting. It’s not related to disease. With samples from the child and potential father you can prove that a person is that child’s parent. 

You can get a genetic test at any age. You can even get a prenatal test if you fear that your baby may inherit a particular genetic condition.  

There is some overlap between ancestry and medical genetic testing. For example, more studies are finding links between markers that indicate particular ancestries and risks for certain diseases. However, the science behind this is still in development. Consumers and sometimes even doctors are at risk for misinterpreting this information. It’s important to not over-interpret the data you get from genealogy tests by treating it the same as medical DNA testing. 

The accuracy of a DNA test depends on the kind of test and service. Medical tests, such as paternity and carrier testing, can give you results with 100% accuracy. 

DNA testing to discover ancestry and ethnic makeup is less accurate. The same company, for example, may give you and your siblings dramatically different ethnicity percentages, or you may get very different ethnicity percentages if you use two different services. This is because there's no one right way to divide and categorize humans. 

Each service will use a different algorithm and have a different set of reference genomes that they use to define particular ethnicities and geographic regions. For the most part, these tests are good at identifying large and geographically distinct ethnic groups, such as the broad categories of Native American, Sub-Saharan African, or Latin American.

But these same databases are not good at telling apart other populations that have been in close proximity for hundreds or thousands of years. French people, for example, will frequently be found to have British ancestry from a mistake in the programs.