In some families, cousins are just cousins. In genealogy, however, we like to get specific. And in genetic genealogy, the exact nature of a cousin relationship is extremely important. You share a different amount of DNA with each type of cousin. So what is a first-cousin once-removed?
A first cousin is the child of a sibling of one of your parents. That is the cousin relationship that we are all most familiar with.
First cousin once-removed explanation
A first cousin once-removed is the child of one of your first cousins. Or the first cousin of one of your parents. The “once-removed” comes from the fact that one of you is one generation further away from the common ancestor than the other one. If two cousins are of the same generation (i.e. the same number of generations away from the most recent common ancestor), then they are just “first” cousins (or third, fourth, or fifth!). Once there is a generational difference between two cousins, then the cousin is “removed”.
Degrees of cousin relationships
It gets a little more confusing when you start to add more generations between you and your cousin’s Most Recent Common Ancestor (MRCA).
In the graphic below, the “kids” are all first cousins.
A second cousin, for example, is when your MRCA is your great-grandparents. A third cousin is when your MRCA is your great-great grandparents. These are called “degrees” of cousins.
A quick rule is just to add “1” to the number of greats to figure out the cousin degree. For example:
- If you share great-grandparents, you are 2nd cousins (1 great +1 = 2)
- If you share great-great grandparents, you are 3rd cousins (2 greats +1=3)
- If you share great-great-great grandparents, you are 4th cousins (3 greats + 1 = 4)
And so on, and so on, forever!
In the graphic below, Bob and Jo are second cousins, since they are both great-grandchildren of Bob and Maria.
If Bob and Jo each get married (to someone else, of course!) and have children, their children will be 3rd cousins to each other. You can see a visual example of this in the next graphic below.
What does generations removed mean?
It’s relatively easy to understand degrees of cousins, but what about when two cousins are not in the same generation? This is when you hear “once removed” or “three times removed”, or any number of generations removed.
How to Figure out the Generations Removed?
Remember that the degree of cousins starts with the cousin that is closest to the MRCA. Then, you count how many generations they are away from the other cousin to get the generations removed (i.e. the difference in their generations).
Take this graphic for example:
These are some cousin relationships, along with explanations, from the family depicted in the graphic:
Paola and Jo are 2nd cousins once-removed. To calculate this, we need to figure out first that Jo is the family member who is the closest to the Most Recent Common Ancestor (Bob and Maria). Bob and Maria are Jo’s great-grandparents, so we will add “1” to the great and say they are 2nd cousins. She is one generation away from Paola – in other words, once-removed, which together is 2nd cousins once-removed.
Paloa and Sam are first-cousins three-times removed. This is because Sam is only one generation away from Bob and Maria (first cousins) and he is three generations away from Paola.
Two real life examples
Most of the time we hear first/second cousins once or twice removed being discussed. And it’s true – those are the most common. That said, it is possible to have a first or second cousin – living – and two or three times removed.
I was recently in contact with a Dutch relative. His grandfather was the youngest brother of my great-great grandfather (b. 1863!). This makes us 1st cousins twice removed. It was really neat to get in touch with him, as his grandfather stayed in Holland and my great-grandfather came to US. I had always wondered about the branches of the family that stayed behind – and he had always wondered about the branches of the family that came to the US. It was a cool experience to talk about that.
The second example is a relative of mine who recently passed away. She was 92 years old, and was the granddaughter of my great-great-great grandmother (b. 1861!). I thought that this was especially fascinating, since she remembered stories about her grandparents. She was my first-cousin three-times removed. This is because she was the grandchild of our MRCA, but was three generations removed from me.
Is it too much work to do all of that calculating? I agree! That’s why I prefer to use this “cousin relationship calculator“. It’s free and easy – just my style.
DNA and Cousins-Removed
For each degree and generation removed two cousins share with each other, they will also share less DNA. If you have a cousin match who doesn’t seem to fit in the typical range, it could be a cousin who is a generation or two removed – especially when it is a 1st or 2nd cousin, as those ranges are relatively set.
Does my explanation make sense? Did it leave you with more questions? Have you encountered any wild cousins-removed relationships? Let me know in the comments!
Thanks for stopping by.