What is a first-cousin-once-removed (1C1R) or a second-cousin-once-removed (2C1R)? In these abbreviations, “R” means “removed.”
Once you understand what “removed” means, it’s really simple, but until then, it’s confusing.
Let’s start with first cousins.
First cousins share common grandparents. Jane and Mark are first cousins. Their parents are siblings.
“Once removed” means one generation offset, or the child of someone in that cousin generation.
Let’s say you’re Jane.
Your child, Jim, is the first cousin once removed to your first cousin, Mark. Said the other way, Mark is a 1C1R to Jim.
Jim and Mark are first cousins once removed.
Flipped around, so that we are comparing Mark’s child instead of Jane’s – Mark’s child, Maurice is a 1C1R to Jane.
Julie and Maurice are both the children of people who are first cousins to each other. They share Steve and Shirley as great-grandparents, so they are second cousins to each other.
Now let’s say that Julie has a son, James.
James and Maurice are second cousins once removed, because they are a generation offset from one another. James is the child of someone who is second cousins with someone else. In this case, James is the son of Julie who is a second cousin (2C) to Maurice.
Now, James has a child, Jill.
Jill and Maurice are second cousins twice removed, because they are another generation offset, or on down their branch of the tree..
Calculating “Removed”
Taking this one step further, Jill is a first-cousin-three-times-removed (1C3R) to Mark.
Cousin relationships are easy to calculate.
Look at the two people you wish to compare. In this case, Jill and Mark.
Find their common generation level. Looking back up Jill’s tree, we find Jane at the same generational level as Mark. Jane and Mark are first cousins (1C). That’s the base relationship before calculating the number of generations your target people, Jill and Mark, are “removed” from each other.
Beginning with the generation below Mark, count how many generations below first cousins Jill is “removed” from Mark.
In this case, in the column at right, you can see that the Julie/Maurice generation is “1”, followed by the James generation at “2” and Jill is generation “3.” Hence, Jill and Mark are 1C3R to each other.
Don’t confused a first-cousin-once-removed (1C3R) with third cousins (3C).
Third cousins would be James and Matthew. Fourth cousins would be Jill and Madison.
It’s easy to calulate the relationship of any two people in your tree.
I wrote about my “chicken scratch” method of calculating relationships in the article, Quick Tip: Calculating Cousin Relationships Easily.
DNA
As you might expect, the amount of expected shared DNA between two people who are second cousins (2C) and second-cousins-once-removed (2C1R) is different, because the DNA has been divided once more in James than it has been in Maurice.
In first-cousins-three-times-removed, the DNA has been divided once again in Jill.
I wrote about DNA and relationship predictions, including half relationships and “removed” relationships in the article, Concepts – Relationship Predications.
You can view expected amounts and ranges of shared DNA for various relationships using DNA Painter’s Shared cM Project tool, here.
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