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