I recently discussed how and why you might need to consolidate your clusters when doing the Leeds Method. I also shared an example and went through the process step by step.
But even after consolidating your clusters, some of you will still have more than 4 clusters. In fact, some of you will still have quite a few clusters. But, why? Well, for many of you it’s because you don’t have any—or don’t have enough—2nd cousins.
Why Second Cousins?
The Leeds Method attempts to use 2nd and 3rd cousins to sort your DNA matches into groups of people who are closely related to each other. In a best case scenario, your chart will have 4 clusters with each of your 4 clusters representing a grandparent line. But, most people need 2nd cousins to make this happen. Let’s discuss “why.”
We all have 4 grandparents and 8 great grandparents. Our (full) 1st cousins share a set of grandparents with us. They are either on our dad’s side or on our mom’s side.
If we sort our cousins based on 1st cousins, we would potentially get two groups. One group would represent our dad’s side of the family, and the other group would represent our mom’s side of the family.
Our (full) 2nd cousins share a set of great grandparents with us. They are either on our dad’s dad’s, dad’s mom’s, mom’s dad’s, or mom’s mom’s side.
If we sort our cousins based on 2nd cousins, we potentially get four groups. This is because our 2nd cousins are the descendants of our grandparents’ siblings. And that is why we use 2nd cousins in the Leeds Method.
Since our cousin lists are built on shared DNA, the Leeds Method uses 3rd cousins to fill in some of those DNA gaps.
NOTE: If you know who some of your matches are, you want to skip any who share more than one grandparent with you and use any who share only one grandparent with you! (I’ll be blogging about this next.)
Example
Here’s an example of a Leeds Method chart that has 19 people sharing between 90 and 400 cM. However, instead of the hoped for 4 clusters, this chart has 8 clusters. It also has no overlap. In other words, each person sorted into only one color cluster group.
An example of a Leeds Method chart with a lot of clusters because of few or no 2nd cousins
If you look at the numbers on the left hand column, you’ll see that these numbers are on the low side of the recommended range of 400 to 90 cM. Many of these matches are likely 3rd cousins. If we don’t have 2nd cousins to “tie” our cousins together, we will get more clusters.
Next Step
No matter how many clusters you get, your next step is to figure out what each cluster means. If your biological parents and grandparents are known, you are trying to figure out which grandparent or great grandparent the group represents. If your biological parents or grandparents are unknown, you will want to work with the matches in the group and see how they connect to each other.
I hope this helps! And, as always, feel free to write and ask me your questions!
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