How you’re related to your DNA matches is increasingly possible to puzzle out in 2021! Here are tools at 23andMe, AncestryDNA, Family Tree DNA, Living DNA and MyHeritage to help you build your family tree with genetic genealogy.
Online tools for helping identify your DNA matches have advanced tremendously since I first published an article about this topic three years ago. (My, how time flies!) So here’s an update—with 2021 examples—from the major genetic genealogy websites.
Centimorgans and genealogical relationships
One important measure in our genetic relationships is the total amount of DNA we share with our matches. Currently, all the testing companies are reporting this sum in centimorgans (cMs). Some now also provide the possible genetic relationships to your match, based on your total shared cMs.
Quick definition: What is a centimorgan? It is very tempting to think of a cM just like you would think of an inch or a centimeter, and for all practical purposes, that is ok. But it is actually much more complicated than that. A cM is a actually more like a crystal ball. It is there to help us predict how likely it is that the piece of DNA we are looking at looks exactly like it does right now a generation ago. This in turn helps us calculate how far back we should be looking for the common ancestor between two people.
Shared cM on your DNA testing site
Here’s what your reports of genetic relationships and total cM look like across the major autosomal DNA testing websites. Keep reading for more tips on how to take what the site tells you to the next level.
With AncestryDNA, next to each person in your match list, you will see a summary of your genetic relationship range and how much DNA you share. Click on the summary to bring up a companion chart like the one shown below, showing your possible genetic relationships to this match, as well as the likelihood of each statistically. Keep in mind that for more distant relationships there will be lots and lots of relationships that are all about the same likelihood. (Below, we’ve only shown you the top half of the chart: there are lots more possibilities for my relationship to this match.)
On the main match page for your FamilyTreeDNA* Family Finder results, you will see a genetic relationship range reported in the third column on your match list, followed by the total amount of shared cMs and the size of the biggest piece of shared DNA in the fourth and fifth columns, as shown below.
On 23andMe, you can see the percentage of shared DNA from the main DNA Relatives home page:
Click on that match to see a detail view, which you can expand to see an estimated relationship (and other suggested relationships), a corresponding tree diagram; the total shared DNA in cM and even a chromosome browser view showing where on your chromosomes you overlap with this match:
On the MyHeritage website, the total amount of shared DNA, total number of shared segments AND even the size of the largest segment is shown on the main match page under the title Match Quality:
Click on the question mark icon next to estimated relationships and you’ll see a diagram of your possible relationships like this:
Access the advanced DNA Tools that MyHeritage offers when you sign up for a free 14-day subscription trial.
Known as a test with British Isles-specific ethnicity reports, Living DNA reports total shared DNA and a simple predicted relationship, as shown below. As of June 2023, Living DNA also has a chromosome browser.
Take Shared cM to the Next Level
For those sites that don’t spell out the likelihood of each genetic relationship, you’ll want to consult Blaine Bettinger’s The Shared cM Project chart. Take the total amount of shared DNA you have with a match, and look up that number in the chart to get an idea of what kind of genealogical relationship might best fit the genetics that you see.
For example, if I share 90 cM with my match, we might be 3rd cousins. But we might also be second cousins two times removed. How do you figure out which one? Simply put: DO GENEALOGICAL RESEARCH!
Final tip: if you find that you share only very short pieces of DNA with someone, it’s possible that rather than descending from a recent common ancestor, you both descend instead from an endogamous community, or one in which people intermarried a lot and therefore had a lot of shared DNA. Learn more about endogamy.
The Ultimate DIY DNA Learning
Sometimes the best way to learn more about how you are related to your DNA matches is by contacting your matches directly. That’s why we’ve put together a free guide with our best tips on contacting your DNA matches. It even includes a free message template you can use to reach out to your matches.
An older version of this article appeared on genealogygems.com.