Are you curious about the number of DNA matches that you have? If you have tested your parents, you might wonder why you don’t match all of the people that they do. You might have noticed that both your mother and father have DNA matches that you don’t have – and it might not make a lot of sense. If both you and your parent are related to someone, shouldn’t all three of you share DNA?
In this post, you will learn:
- Why you won’t have all of the same DNA matches that your parents have
- Why you might have DNA matches that your neither of your parents have
- Why you can’t always count on shared matches with your mother or father to figure out which side of the family your DNA match is on
Why don’t have all of the same DNA matches that my parents do?
I get this question frequently, but what really led me to write this article was something that occurred to me this morning, when I was looking at my own DNA results on My Heritage DNA. When you manage more than one DNA kit on My Heritage, you can see a summary of all of the DNA tests that are on your account right from your main DNA page. This is what I saw this morning:
The first thing question that came to mind was this: If my dad has 1068 DNA matches, and my mom has 2190 DNA matches, why don’t I have 3798 DNA matches on my list? As you can see, I only have have 2269 DNA matches. What is the meaning of this? Am I not related to all of those other DNA matches that are on my mother and father’s list?
The answer is fairly simple: Yes, I am related to all of the people who my mother and father are related to – in a genealogical sense. If someone is related to my father, for example, I am also related to them. We share a common ancestor, and share a branch, if you will, of our family tree. The matter gets complicated when you introduce DNA, however. We can share an ancestor with someone, and truly, legitimately, be related to them, and yet have no genetic material in common.
(It should be noted that all humans share a lot of DNA, but the type of genes that I am referring to are the ones that are unique to each individual – they make up only a small portion of our total DNA, but the differences are strong enough to distinguish one person from another.)
I inherited 50% of my DNA from each parent to make up my full genome. What this also means is that I only inherited 50% of each parents’ DNA. There was 50% of the DNA of each parent that I didn’t inherit. So the primary reason that my dad and my mom have DNA matches that I don’t have is because I didn’t inherit the DNA segments that match those individuals. My parents still have all of their DNA, and so the DNA test is still able to match those segments together.
It’s as simple as that, really. An interesting thing to note on this topic is that my siblings inherited 50% of their DNA from each of our parents, as well, but not the exact same 50% of the DNA that I have. The result of this is that it is possible for my siblings to match some of my parents’ DNA matches that I don’t match – they will have people on their DNA match list that don’t match me, even if we are all related to each other.
Why do I have DNA matches that neither of my parents have
This is a less common problem, but it’s still important to address. There are three reasons that you might show DNA matches on your match list that don’t match either of your parents:
- It’s possible that it is just a bug in the software. I’ve noticed this with Ancestry DNA. Sometimes, if neither of my parents show up as a shared match, I will see them still on my parents’ match lists. It’s just a fluke and no further attention should be paid to it.
- It is possible to have a DNA segment that is “coincidentally” identical. In the genetic genealogy world, this is called “identical by state”, meaning that it just “is” identical. This is most likely to happen with very small DNA segments (less than 5 cM in length), but can happen every once in a while with a larger segment (there is only about a 1% chance that a 11 cM segment is coincidentally identical). It’s exceptionally rare to have this occur with segments larger than 15 cM, and it would also be statistically improbable to have more than one identical by state segment larger than 5 cM with the same match.
- It’s possible to be related to someone on both sides of your family. You can be related to someone in more than one way, and sometimes, if you are only distantly related on both sides, it’s possible that the segments that your parents share fall below the matching threshold set by your testing company, but when you have them together, like you do, it shows up as a match. This would only happen with really small segments (fairly distant relatives)
There are all sorts of crazy scenarios in the DNA world, as you can see.
Why you can’t always count on shared matches with your mother or father to figure out which side of the family your DNA match is on
This might seem clear to you by this point, but it is still worth discussion. When trying to figure out how a DNA match is related to you, many people will use whether they share the match with a mother or father in order to determine, conclusively, which side of the family the match falls on. While this is often a useful method, it is not foolproof. You could be related to the match on both sides of the family, and perhaps one of your parents did not inherit a DNA segment that matches this relative. The bottom line is that the “old fashioned” genealogical research methods are the best way to prove a relationship to someone*, especially when trying to figure out a more distant relationship.
*The exception to this rule is a very close relationship, like parent/child, close or immediate family. The amount of shared DNA in these close family relationships leaves little to dispute.
I hope that this post has helped you understand a bit more about how DNA is inherited, why your parents will show different numbers of DNA matches and match people that you don’t. If you have any questions, concerns, or just want to share your story, please feel free to leave me a comment below.
Thanks for stopping by!