WTCB Issue – Alt MRCA


I have a number of cases where the Match has an MRCA, but Clusters with a different group of Matches who clearly have a different MRCA and/or TG.  Example: A Match who has an alternate MRCA which doesn’t align with a TG. I discount the MRCA because the shared DNA segment with the Match could not have come from that MRCA. Some have a paternal TG and a maternal MRCA; some are clearly from different grandparents on the same side. I now have found two examples of such a Match who Clusters with other Matches who share the MRCA but not the TG. It is not unusual for a Match to have more than one MRCA from Colonial Virginia, but usually one is closer and the closer MRCA has a much higher probability of being the one who passed down the shared DNA segment. But “higher probability” does not mean always.  

My latest example is a Match with TG [01Y36] 14.0cM (on my mother’s side], but over half of the 23 Shared Matches have TG [17D25] (on my father’s side). [17D25] is a pretty well-established TG for me with an MRCA of A0170P (my CANNADAY/HILL ancestral couple at the 6C level). So I checked my Notes and found the Match has a ThruLine to CANNADAY/HILL. That explains why the Match Clusters with other Matches with MRCAs of A0170P.

Bottom line: Although my main objective is deep Chromosome Mapping, the ultimate goal is to get the genealogy right. In this case I want to also figure out the [01Y36] MRCA, so I must remove this Match from the A0170P-[17D25] Cluster. I also have to remind myself to follow the data – the data is talking to me, I need to listen…

[19Nb] Segment-ology: WTCB Issue Alt MRCA by Jim Bartlett 20220926

Segment Data for Ancestry Matches 2


A Segment-ology TIDBIT

My first post with this title (here) listed 4 ways to get Segment data for AncestryDNA Matches; and then added another way using GEDmatch.

Here is yet another way.

In Walking The Clusters Back (see WTCB 2022 and WTCB SITREP) I’ve now completed the analysis of all Matches over 20cM – almost all fit into one of several hundred Clusters. I’m now integrating the below 20cM Matches who have segment data (a TG ID), usually from GEDmatch – over 800 of them. Most of them have Shared Matches which usually provides a consensus on the Cluster.  In checking my Master segment spreadsheet (with all of my Match Shared Segments), I noticed a number of AncestryDNA kits which didn’t yet have a link to an Ancestry profile. It turns out that usually all the Matches with the same TG ID will be in one Cluster. It is a relatively easy task to find that Cluster (particularly with WTCB) with some of the Matches – and then review the few other TG Matches with the other Matches in that Cluster. I usually send a message to the Ancestry Match to confirm they indeed uploaded to GEDmatch (and promise to help them with the DNA if they are).

Result: more AncestryDNA Matches linked to specific DNA segments (TGs).

[22BJ] Segment-ology: Segment Data for Ancestry Matches 2 TIDBIT by Jim Bartlett 20220223