Extending the MRCA of a TG through Clusters

A Segment-ology TIDBIT

Triangulated Groups (TGs) are one way to group your Matches – grouping Matches who share overlapping DNA segments with each other. The DNA segment represented by a TG, is passed down to you from one of your parents, and from more distant Ancestors on that side. As we find Most Recent Common Ancestors (MRCAs) with Matches in a TG, we begin to learn which ancestral line passed down the TG segment – a Common Ancestor.

Clustering is another way to group your Matches – grouping Matches who share other Shared Matches with each other. The Matches in a Cluster also tend toward a Common Ancestor.

The companies where Triangulation is possible generally do not have many robust Trees. And so the TGs do not have many MRCAs. AncestryDNA has many robust Trees and a ThruLines tool that determines many Common Ancestors (CAs) , but does not provide the DNA data needed for Triangulation.

Is there a way to combine the best of both worlds? I think there is. TGs and Clusters should be grouping on the same thing – an ancestral line – a Common Ancestor. When a TG and a Cluster clearly have some of the same Matches, I think the deeper MRCAs in the Cluster, can be imputed to the TG.

This is another method of Walking The Ancestor Back (WTAB) in a TG. You already have a TG with some MRCAs along the same line. The Most Distant Common Ancestor (MDCA) in a TG usually represents a couple, one of whom passed down the TG segment. The next generation back has only two possibilities: the paternal or maternal side of the MDCA.

The MRCAs in a Cluster aligned with the TG provide a strong clue in reinforcing and extending the CA for a TG.


[22AP] Segment-ology: Extending the MRCA of a TG through Clusters TIDBIT by Jim Bartlett 20191118

3 thoughts on “Extending the MRCA of a TG through Clusters

  1. Pingback: segment-ology

  2. Jim, I love the way you can simplify complex issues so eloquently! Totally agree, many clusters once the chromosome data is known actually end up in the same TG’s. If you can find one or two across both it does increase your chances of being able to find that elusive CA. Thanks again!


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