Do you want to know what an SNP is in DNA results? In this post, learn all about these variations in our DNA, and how they are used to help us learn about our ancestry.
There are many vocabulary terms, including abbrevations and acronyms, such as SNP, that we see when we begin reading about how to understand autosomal DNA results. Learning the meaning of some of these more common terms is the first step to becoming a beginning genetic genealogist, a person who uses their DNA results to build their family tree.
Even if you are not interested in learning how DNA results can help you learn more about your ancestors, learning about the term “SNP” will help you understand more about what you are reading online when it comes to discussions about DNA results.
What does SNP stand for?
SNP stands for single nucleotide polymorphisms. Scientists use the acronym “SNP” as a shorter way to describe these unique genetic mutations.
If you want to say SNPs aloud, you would pronounce it like you say the word “snips”.
As you probably already know, all members of the same species of organism are genetically very similar. If you compare the DNA of any two humans, we would find that they are about 99.99% identical.
It doesn’t take very much DNA to be very different. For example, you might be surprised to learn that we share over 50% of our DNA with chickens.
Even though any two humans on earth are almost entirely identical, and would likely look entirely identical to aliens visiting earth, we can tell each other apart from others of our species. Contained within the .01% of our DNA that is not the same as others of our species are the genes that make us different from others.
What are SNPs and why are they important?
Scientists know most of the locations in the human genome where two individuals will be different. In other words, they know where to find the approximate .01% of human DNA that is not identical to every other human.
SNPs are locations in our genome where mutations usually occur. They are sometimes known as “copying errors“.
Simply put, this .01% of our DNA is where companies like Ancestry DNA, 23andMe and My Heritage DNA, can examine to find patterns to report our ethnicity estimate and similarities to give us our DNA match lists. We have more than 3 billion locations in our DNA, and only a small percentage of these locations in our genome will be different from person to person.
These locations that tend to vary between individual humans are known as SNPs.
How are SNPs used in autosomal ancestry tests?
The top autosomal DNA testing companies each have a slightly different process for testing SNPs, but each company generally tests at least several hundred thousand individual SNPs in their customers genomes. Some companies test closer to one million locations that are known to have mutations.
Some people mistakenly believe that companies that test higher numbers of SNPs offer better test results, however there is no direct correlation between the number of SNPs tested and the quality of test results. Instead, we should make sure to choose a DNA testing company that has a proven track record in interpreting SNP data.
Any of the top DNA testing companies, such as 23andMe, Family Tree DNA, My Heritage DNA, and Ancestry DNA, offer a reliable DNA testing experience and results that can be trusted.
How are SNPs used to determine your ethnicity?
DNA testing companies have been able to develop complex algorithms that can determine where your ancestors most likely lived based on specific SNPs in our DNA. Their software knows that most people who have ancestors from a specific part of the world show a particular “marker”, or unique sequence of DNA, at a precise location in their genome.
Another way to think about this is that the algorithm can sort DNA testers into groups that have, or do not have, a particular marker at a specific location in their genome.
It is important to know that the science of using SNPs in our DNA to determine where our ancestors likely lived, or their ethnicity, is still developing. This is why we regularly see changes in our ethnicity estimate, such as the regular updates that occur for those who tested with AncestryDNA.
How are SNPs used to find DNA matches?
SNPs can also be used to measure how closely related two people are. While most people are different at the specific known locations in our DNA where the human genome tends to vary, the people who do have identical markers at those locations are likely to be our relatives.
The higher the number of matching SNPs where you are identical to someone else, such as another customer who tested their DNA with the same company, the more closely related you are, generally speaking. We don’t usually see details about SNPs on our DNA match lists, with one exception that I will mention below.
Instead, we usually only see information about the number of centimorgans (cMs) shared between two people. cMs is a term used to describe genetic distance or length of a DNA segment, which describes the genetic distance between the location (SNP) where two people are identical and either the end of the chromosome, or the location on the chromosome where they stop being identical.
It is possible to have only one, or dozens, of places in our DNA where our sequences SNPs match our relatives. When we have many, long DNA segments in common with someone else, they are more closely related.
We typically share only one, small segment with distant relatives. DNA segments shared with relatives were passed down from shared ancestors.
As I mentioned earlier in this article, there is one place where you can see information about SNP data between you and your DNA matches. This is on the free site Gedmatch, where you can upload your DNA file from your DNA testing company.
On the Gedmatch One-to-Many results, which is the equivalent to the DNA match list on the site, there is a column that shows “overlap“, which is the number of SNPs that were compared in the results.
I hope that this post has helped you understand more about single nucleotide polymorphisms and how they are used in DNA testing for ancestry, including ethnicity estimates and DNA matching.
If you have any questions about something that you read in this post, please join in the discussion below.
Thanks for reading today!
Sunday 29th of May 2022
Does that mean people that I share 10 or more DNA Segments with I'm more closely related too ?Does the total number of Shared Centimorgans also to be used for consideration too,or is it just the number of Segments on Ancestry?
Sunday 5th of June 2022
Hi Tim, Generally speaking, the more DNA segments that we share with our DNA matches, the more closely related we are to them. However, it is also important to take into consideration how big those DNA segments are. On Ancestry, we don't usually have access to this information (we only get the largest segment size, which is also very helpful). It is also possible to be distantly related to someone in more than one way (or several ways), in which case we would see many small segments shared. Thank you for your question! Sincerely, Mercedes