27
Mar

What is a First Cousin DNA Match?

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Our DNA match lists can be overwhelming sometimes, especially the first few times you examine it.  If you got your DNA test results back and you have a first cousin match, this post will help you understand what a first cousin match really means and how this person might be related to you.   Whether you are looking for biological family, or know most of your family and have a mysterious first cousin match, or just want to know what a first cousin match would like like on your results, you’ll learn something here.

What does a first cousin match look like on my DNA results?

Depending on which company you test with, your first cousin match will look slightly different.  You’ll notice that each company has a “relationship range” that they include along with the general category of first cousin.  Additionally, you will observe that each of the relationships within the relationship range is a relatively close relationship (first or second cousin, uncle, half-brother, nephew).  A first cousin match is a great match!

If you tested with Ancestry DNA, the first cousin category is one of the closest categories (after parent/child, immediate family, and close family).  On Ancestry DNA, your first cousin match will appear like this:

What does a first cousin match look like on ancestry

Family Tree DNA also categorizes your DNA matches according to estimated relationship, though they are not separated (they appear in your long list of matches).  If you did your test with Family Tree DNA, your first cousin match will show up like the image below:

What does a first cousin match look like on Family Tree DNA

And finally, if you tested with My Heritage DNA, your first cousin match might show up something like this:

What does a first cousin match look like on my heritage dna
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Is my first cousin match really a first cousin?

Since most of the testing companies include a few possible relationships, or even a range of relationships along with your first cousin match, you might have guessed that there is a possibility that your first cousin match is not really a first cousin, but instead another close relationship.  If you guessed this, you are 100% correct.

As it turns out, there is no way for your DNA testing company to be able to tell you exactly how you are related to someone simply based on DNA (other than a parent, child, or identical twin).  This means that we will have to employ other methods to determine exactly how we are related – more on this below.  All we really know is that your first cousin match could be an actual first cousin, or some other similar relationship.

How do testing companies determine the estimated relationship?

The way that the DNA testing companies determine that someone might be a first cousin is based on your amount of shared DNA, along with the number of DNA segments that you share, and the length of those DNA segments.  The amount of shared DNA between two full first cousins is generally accepted to be between 575-1300 centimorgans (cMs).  If you share DNA with a match that falls within this range, the match is likely to get placed into the “first cousin” category on your DNA match list.

Note:  Each company has a slightly different threshold for how much DNA two matches would share to be placed in the first cousin category, so for the purpose of this post, I’m using shared DNA as our guide.

The reason that a first cousin match can be tricky is because there are several other relationships that fall within the same range of shared DNA:

  • Half aunt
  • Half uncle
  • Half nephew
  • Half niece
  • Great-grandparent
  • Great-grandson or great-granddaughter

To make matters slightly more complicated, there is always a small chance that the amount of shared DNA with your first cousin, or any other relative, could fall slightly out of the usual range.  For example, my father has a first cousin who only shares 520 cMs with him.  I am 100% sure that he is my father’s full first cousin, since both of the parents of the cousins (my grandmother and great-uncle) have tested and share DNA as full siblings.  This is an unusually low amount of shared DNA for full first cousins and is not very common, but it’s still good to know that it is possible.

Generally speaking, if you have a first cousin match, you should consider the relationship possibilities that I listed above, unless there is strong evidence (including additional DNA evidence involving other family members) that the relationship is slightly closer or more slightly more distant.  It would be impossible* for the relationship to be more than one more degree of separation closer or more distant, however.

* I use the word “impossible” here with hesitation!

How can I tell how my first cousin match is related to me?

Since the exact relationship with your “first cousin” match could range from great-grandparent to half-niece to actual first cousin (and anywhere in between), you will have to do a little DNA sleuthing to learn more.  The more you know about you know about your family tree, and the more DNA matches you have, the easier it will be.

(If you know you need to get more DNA matches or you just want more matches, read about other websites where you can upload your DNA)

Figure out who your common ancestors are

One thing that you should think about with a first cousin match is who your common ancestors might be.  For just about every relationship in the first cousin range (575-1300 cMs), your common ancestors are at least one of your grandparents.*  Full first cousins will share both grandparents, but for half-aunts, half-uncles, half-nieces, and half-nephews, you will share one grandparent only.  Of course, the exception to this would be if your first cousin match is your great-grandparent, or great-grandchild.

*First cousins once-removed, half-first cousins, and half-great nieces/nephews, or half-great uncles/aunts can share more than 575 cMS (as high as about 650 cMs), so if your match falls within this overlap range, there is a chance that your common ancestors are one generation back (great-grandparents).

Here are some hints that might help you figure out how your first cousin match is related to you:

  • Do they have a family tree, and if they do, do the surnames match those of your parents or great-grandparents?
  • Determine which side of your family that they are on by viewing shared matches, or matches that you have in common with them.  For example, a person who is related on your mom’s side of the family will not have your dad’s first cousin as a shared match.
  • Once you know if they are on your mom or dad’s side, try to figure out which grandparent on your family tree your first cousin match would also match.  You can learn this information from viewing your shared matches and their family trees.  You should be able to spot surnames in common with your surnames in their family trees.
  • If you have figured out exactly which line of the family they are on, you then should try to figure out how old they might be (perhaps by viewing the birth dates of their parents or grandparents in their family tree to get an approximate age).  This helps eliminate relationship possibilities to narrow down the options.
  • Check out the geographic locations of where their parents, grandparents, and great-grandparents were born and where they lived.  This could give you a clue that matches geographic locations in your own tree.
  • Lastly, you could consider contacting your first cousin match.  A polite and friendly note goes a long way.  Read here about best practices for contacting DNA matches.

But what if you don’t know your family tree?

If you are adopted, or don’t know who one of your biological parents is, it’s definitely going to be a little more challenging for you to figure out how a first cousin match is related to you.  I would recommend following as many of the steps in the previous section as you can, including uploading your DNA to other sites to get as many DNA matches as possible.  Remember that for a first cousin match, you are looking for grandparents, at the furthest, in common with your match, so you should be looking among DNA matches for relatively recent common ancestors that they share in common with other closer matches.

I would caution that if a group of siblings test, it can “skew” this type of reasoning, since several siblings will share the same family tree, so if you notice that your matches might be siblings, try to find other matches outside of their immediate family group to verify your line of thinking.

Conclusion

I hope that this post has given you some helpful hints about what first cousins matches look like on the various testing sites, and how to figure out how your first cousin DNA match might be related to you.  If you have any questions about anything that you read here, or just want to share your experience, I would love to hear from you in the comments.

Thanks for stopping by!

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What is a First Cousin DNA Match?
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What is a First Cousin DNA Match?
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Whether you are looking for biological family, or know most of your family and have a mysterious first cousin match, or just want to know what a first cousin match would like like on your results, you'll learn something here.
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Who Are You Made Of
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