Who is in a cluster? And how are they related to you? I recently wrote about “Who Is in a Cluster?” and introduced the concept of Mountains and Valleys. I think a better term is the Venn Diagram Effect. This post continues to explain and illustrate that concept.
As I mentioned in my last post, when we cluster our DNA matches using either the Leeds Method or an automated adaptation, we usually expect all of the matches in a cluster to be descended from one couple or individual and we expect all of the matches to be related to each other. But, this is not always the case. And yet, the results when this is not the case are still incredibly helpful!
For now, let’s talk about the original range of DNA matches when doing a Leeds Method chart: 90 to 400 centiMorgans (cM). In this range, most people’s DNA matches will be 2nd and 3rd cousins (including those once removed, twice removed, etc.)
Below is an example of a cluster that has been diagramed which shows that all of the DNA matches are descended from one couple – the test taker’s great, great grandparents – and all of the DNA matches are related to each other.
But sometimes, we get a cluster like the one diagrammed below. In this case, not all of the DNA matches are related to each other. The 3rd cousin (3C) on the far left is not related to the third cousin once removed (3C 1R) and the third cousin twice removed (3C 2R) on the right. Additionally, not all of the matches are descended from one couple. Instead, they descend from two sets of the test taker’s great, great grandparents. These two sets of great, great grandparents are the two sets of parents of the great grandparents shown.
Instead of relationships, the cluster diagram below adds names to those ancestors. This cluster contains 2nd cousins, but it also 3rd cousins from both sides of that family line. In this example, the DNA matches include both descendants of Mike & Sally – the test taker’s 2nd cousins – but also descendants of Mike’s parents and descendants of Sally’s parents. These descendants are the test taker’s 3rd cousins.
Below is a Venn Diagram. Both circles represent 3rd cousins, though one is on the paternal side of the great grandparent couple and the other is on the maternal side of the great grandparent couple. The intersection includes the 2nd cousins. But, it also includes the test taker. This can be valuable for those working with unknown parentage who can now easily identify a likely great grandparent couple!
Lastly, I’m combining a cluster diagram with the Venn Diagram circles. If you diagram a cluster and see this Venn Diagram Effect, hopefully you will now have a better idea of what it represents!
Please let me know if you have any questions!
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