More often than you might expect, people are surprised by their DNA results. It can be disappointing or shocking to expect someone to be genetically related to you, but find out that they are not. This article discusses reasons what it means if a first cousin does not show up on your DNA match list.
This particular paragraph addresses people who have tested with Ancestry DNA:
It can sometimes take a few days for your matches to “populate” on Ancestry. If you just got your test results back today and you don’t see someone that you are expecting to see on your match list, I would recommend waiting for a few days before coming to any definite conclusions. I have not seen this issue on Family Tree DNA, so if you tested with that company, your match list is usually ready as soon as you get your results e-mail.
Is it possible for first cousins to share no DNA?
First cousins will always share DNA. It’s true that with every generation of descendants a little less DNA is inherited from the common ancestor (or pair of ancestors, like grandparents in the case of first cousins), but in the case of first cousins, so much DNA is shared by their parents, whether they were full or half-siblings, that it is statistically impossible for first cousins to share no DNA.
How much DNA should first cousins share?
Even though first cousins will always share DNA, the amount that they can share can very dramatically. There will be more DNA shared by full first cousins than there is by half-full cousins. It’s completely normal to have this wide range of shared DNA, since DNA is inherited randomly from each parent, there is no way to know or control which DNA is inherited. The only thing that is important to renumber for this discussion is that first cousins always share DNA.
Full first cousins (cousins whose mother or father were full siblings to their cousin’s mother or father)
These cousins will share an average of 12.5% DNA. Using centimorgans (cMs) as a measurement, this means that first full cousins will share between 535-1330 cMs.
(Click here to find out how to find shared centimorgans on AncestryDNA)
Half-first cousins (cousins whose mother or father were half-siblings to their cousin’s mother or father)
Half-first cousins will share an average of 6.25% DNA, or between 215-650 cMs.
What does it mean if my first cousin doesn’t match my DNA?
The most common result that people find when they look at their cousin matches is that they share less DNA than they expected with their first cousins. This usually means that their parents were not full siblings (see DNA shared between half-first cousins above). When there is no DNA shared, however, it means one of two things:
- One of the first cousins belongs to a different genetic family
- One of the parents of the first cousins belongs to a different genetic family
In order to figure out which of the above situations is most likely, you should look at the DNA results of both cousins and look for the following clues:
- Does either cousin have close family matches who are in the biological family that you were expecting them both to belong to?
- Do you see familiar surnames in the family trees of either of the matches?
- Are there close matches on the DNA list that you don’t recognize?
There are a few rare medical treatments (like a bone marrow transplant) that can cause unexpected DNA results, so this is something to keep in mind before discussing any conclusions that you have about your DNA list with family. Obviously, finding out that someone is not a genetic match to you can be a very sensitive topic, and I recommend proceeding with caution when deciding what to do with your newly-discovered knowledge. It is also completely acceptable to keep this particular knowledge to yourself, if you feel like it is most appropriate to do so.
Pro tip: Most importantly, we consider those who we love to be family – so don’t let the amount of DNA that you share with someone affect your relationship, or how you feel about them.
Can the test results be wrong?
I have never heard of a Family Tree DNA, Ancestry DNA, or 23 and Me test results be wrong when it comes to a family match. The only times when the test has been “wrong” has been in rare circumstances when there have been medical treatments that would affect these types of DNA tests. Read the 23 and Me note about bone marrow transplants, for example.
If you did not test with any of the above DNA companies and you are surprised by your results, I would recommend testing again with one of the “big 3” DNA testing companies before you come to any definite conclusions.
Having more relatives do a DNA test is a great way to figure out why your cousin doesn’t match you
If, after careful examination, it does appear that your DNA results are correct (and that your cousins are, too), which they most likely are, the next thing that you might want to do is try to figure out why. You don’t have to, but many people like to try to determine whether what they know about their ancestry is accurate.
The best way to do this is to have more family members do DNA tests. Older family members are the best people to test, with their knowledge and permission, of course, because their DNA will provide the most helpful information.
It’s best to do additional DNA tests with the same company that tested you and your cousin’s DNA. This way, everyone shows up in the same database and you can see which matches everyone shares in common and exactly how much DNA everyone shares with another.
You can use this link to order your Ancestry DNA kit: Discover the story AncestryDNA® can tell. I may get a very small commission at no extra cost to you, which helps me support this website. Thank you!
I hope that this article has helped you understand how much DNA first cousins typically share, and what it means when first cousins share less DNA than expected. If you have any questions about anything that I mentioned, or would like to discuss your particular DNA results, please leave a comment.
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