How to Understand Your AncestryDNA Test Results (Even If You’re Confused by Cousin Matches) — Part One
Doing a DNA test is super exciting. It’s a great way to learn about your ethnic origins, but it gives you so much more than that. I find people often see their ethnicity results and get excited by some of those findings. But then they take a look at the cousin matches and stop right there in their tracks. All of a sudden they see a bunch of names they don’t recognize, and terms like “2nd cousin 2x removed” and “108cM shared.” What does this all mean?
By learning a few basic DNA concepts those cousin matches will start to make sense, and likely open up new discoveries in your genealogy journey. This guide will help you to understand your AncestryDNA test results, but these basics apply to most DNA testing companies.
What Your Ethnicity Estimate Really Tells You
DNA testing companies like Ancestry, MyHeritage, and 23andMe analyze and compare your 22 base pairs of chromosomes, intentionally excluding the X or Y chromosome (there are other tests specifically for sex chromosomes.) For each chromosomal pair, you inherit one chromosome from your mother and one from your father. Your DNA is compared to millions of other users in the testing company’s database, providing an analysis on your ethnic origins and genetic relatives who have also tested with that particular company.
Ethnicity estimates are a dynamic feature in the sense that they will change over time, which is completely normal. The estimates are created by comparing your DNA sample to reference populations with very well researched and established genetic lines that originate from a particular area. The amount of your DNA that matches the reference populations will determine how much of an ethnicity you have. This can change over time as more reference samples are added to a database, since with more comparisons these tests will become more accurate and more specific sub-regions will emerge.
Even though you inherit exactly 50% of your DNA from each parent, you don’t necessarily inherit exactly 25% from each grandparent, 12.5% from each great-grandparent, and so on. The DNA you receive from each parent is a random mix of the genes they received from their parents. In turn, you receive a random amount of ethnicity from each grandparent.
Here’s a simplified example. Let’s say all of your grandparents have 100% pure ancestry from the areas they come from. Your paternal grandfather is 100% Irish, your paternal grandmother is 100% Italian, your maternal grandfather is 100% Scottish, and your maternal grandmother is 100% Dutch. Your mother will be 50% Irish and 50% Italian, and your father will be 50% Scottish and 50% Dutch. But your results could look like this:
23% Irish
27% Italian
21% Scottish
29% Dutch
For this exact reason, you and your full biological siblings may have slightly different ethnicity results. This is perfectly normal, and actually helps to reveal the many different ways that your DNA is unique to you! You might even have low percentages of ethnicities that you don’t share with each other, which could be explained by this too.
For example, I have about 2% West African ancestry, which I have been able to trace to a maternal 4th-great-grandmother who was a plantation slave in Jamaica. It’s very likely that one or more of my four siblings has none of this ethnic heritage since it’s such a low amount for me and it has a distant origin.
What are centimorgans (cM)?
Simply put, a centimorgan (often abbreviated as cM) is a unit of measurement that represents how many base pairs of shared DNA there are between cousin matches. Since these tests analyze your first 22 pairs of chromosomes, they will compare how many cM you and others in their database share across those pairs. The number of shared cMs help us to determine how closely matches relate to one another and what the likely relationship is between two people. The more cM you share, the more closely related you are to that person.
How to Interpret Cousin Matches
Here’s an example using my own AncestryDNA matches. The top three matches on my list are my paternal grandmother, one of my dad’s first cousins on his paternal side, and one of my mom’s first cousins on her paternal side. These results help to illustrate some common points where people will get confused, but really it’s just the way that Ancestry presents the information.
Let’s start with my Gramma (she’s the person who got me into genealogy as a hobby!) Her and I share 1,413 cM, which is about 20% of our DNA. Just like I mentioned earlier, genetic inheritance is random so it’s very unlikely that you would get an even amount of DNA from each grandparent. Since I share 20% of my DNA with my dad’s mother, that means I would share 30% with his father. That’s just the random mix of my grandparents’ genes that I received from my dad.
My next two matches are my parents’ cousins, so my first cousins once removed (or 1st cousins 1x removed as Ancestry displays it.) This is a great example of how you can share different amounts of DNA with different people despite the relationship being the same.
In these match examples, the most recent common ancestors (MRCAs) for both matches are my great-grandparents (by parents’ grandparents.) With my dad’s cousin we share 650cM, and with my mom’s cousin we share 423cM. It appears that I received more DNA from my paternal great-grandparents (supported by the lower amount of shared DNA with my grandmother) than I did from my maternal great-grandparents, which is totally normal. So you can have the same relationship with two different people, but very different amounts of shared DNA.
This example also shows something that Ancestry does that often confuses people. My third match, my mom’s 1st cousin, is displayed as either “1st cousin 1x removed or half-grandaunt.” Because the amount of shared cM for each kind of relationship varies due to random genetic inheritance, ranges are determined to set the parameters for what kind of relationship it is. 423cM fits within the range of 1st cousin 1x removed, but also in the range for half-grandaunt. Ancestry’s algorithm can’t determine the exact relationship, but it will give you a “best guess” that sometimes includes two options.
If you see a match pop up and you know the relationship between you, and Ancestry is showing a different relationship possibility, it’s best to double check that the relationship you believe to be true is in range (it often is.) I highly suggest using this tool, The Shared cM Project by DNA Painter, to check relationship probabilities. The relationship that you know is most likely correct if it falls within range, but it’s still worth checking.
Tips for Moving Forward With Your DNA Matches
Now that you understand the basics, it’s time to start looking over those matches and discovering how they fit into your tree. This is where traditional and genetic genealogy really start to overlap. I suggest building out as much of a tree as possible based on genealogical sources like censuses and vital registrations, then cross-referencing your tree with your matches. It’s definitely a marathon and not a sprint, but utilizing DNA is a fantastic way to discover more about your family history—and even break through the toughest brick walls.
Understanding your DNA results is the first step toward uncovering meaningful stories in your family history—but you don’t have to figure it out alone. If you’re feeling stuck or overwhelmed, my DNA research services are designed to help you make sense of your matches and take the next steps with confidence. Explore DNA packages here or book a free consultation to talk through your options.
