A Segment-ology TIDBIT
Up Front – it’s the one with the highest average cM among Match cousins.
Setup: You’ve pretty much determined a particular couple are bio-Ancestors to youself (or someone else) – often by a consensus of Match Trees in a group (usually a Cluster) – see here. However, this bio-couple had a number of children. Which one of them was the bio-Ancestor? It gets harder and harder the more generations back you are researching.
Process: I’ve had good outcomes by determining as many DNA Match cousins as possible for the bio-Ancestor couple. Line up the DNA Matches and the shared DNA cMs under each of the children, and then determine the average cM for each child. In general, one of the averages will be somewhat more than the others – even when you don’t know the link. That’s because you are a closer cousin with Matches who descend from the same child as you do. For instance, you may be a 5C through most of the children – sharing an average of 25cM with those Matches; and you would be 4C with the Matches who descend from then one child who is your Ancestor – sharing an average of 35cM with them. Of course, our results may vary somewhat from the Shared cM Project, but it’s the concept we are focused on here.
When I do this analysis, I drop down into the smaller segments, in order to get a fair comparison among all the cousins I can find. The more Matches we use, the more it averages out to the Shared cM Project and the correct bio-Ancestor child.
[22CI] Segment-ology: Which Sibling Is the Bio-Ancestor? TIDBIT by Jim Bartlett 20240403
segment-ology 
Ciao jim sono kevin ricordi,ho fatto testare mia madre e quel gruppo che ti ho parlato tante volte non e uscito nei risulta ti di mia madre ero convinto che era da parte materna ma mi sono sbagliato.adesso rimane solo mio padre puo darsi che e a lui ho pure potrebbero essere falsi.che dici grazie.
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Kevin, That is great news that you now have your mothers DNA tested now. And since you know that group doesn’t match her, there are only two options – paternal side or false segments. If you Triangulate the segments (over 7cM) they are usually true. If they don’t Triangulate, they are false. Jim
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Ciao jim kevin.si hai ragione adesso ho e paterno ho sono false.pero ce una triangolazione oltre il 7cM e poi ci sono anche il 9 e 9,4cM.pero ti ricordi che dissi che queste corrispondenze finivano ho iniziavano quando un altro segmento che era paterno cominciava e li che avevo il sospetto che qusto segmento sconosciuto di quel gruppo finiva mentre cera questo segmento che e paterno pro punta e punta.io mi sono accorto dopo che ho fatto testare mia madre se no facevo fare test prima ha mio padre.pero ce un altra cosa che ti ho parlato che parecchie corrispondenze di questo gruppo sconosciuto avevano stessi inizi di numeri rs e anche finale con corrispondenze che so che sono paterne.e strano.
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Kevin, Yes it may be strange, but such is life with the DNA segments. It is entirely possible that some of your paternal DNA segments end, and another paternal DNA segment begins. That often happens at a crossover point – perhaps between DNA from your father’s father and DNA from your father’s mother. There are many combinations when you consider all the generations of DNA you get from your Ancestors. Good luck sorting it out. Jim
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Kevin.jim ho notato che quel gruppo sconosciuto hanno certi stessi numeri posizione iniziale posi finale rsid iniziale rsid finale uguali e ha un gruppo di 5persone che sono paterni ma da parte di mio nonno paterno ohay.grazie per il fastidio ma e molto strano.
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Kevin.ho un segmento che e nonna paterna che e propio adiacente sia ha quel gruppo che ti parlo sempre e adiacenti ha un segmento che e nonno paterno,poi ho un segmento che e nonna paterna sempre sul.16 ma il lato sinistro di quel gruppo sconosciuto ha un altro segmento sempre sul 16 ma sinistro e si sovrappone con corrispondenze di nonna paterna.
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Thanks for the feedback – please let me know if your review works out.
As for the MRCA comment – it depends on the number of generations back to the MRCA – if all the generations are the same, then the relationships are the same; but if some go back 7 generations and some 8 generations to the same MRCA, then they are once removed from each other and the cM “should” be a little different.
Jim
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Interesting idea. It makes sense. I will be interested in exploring this with my own data, although I am reasonably sure in the groupings which one is my own ancestor. However, exploring this will be worthwhile as it might be one more clue in a future situation, or for others that I help. We try to develop a preponderance of evidence, so it is always helpful to have an additional analysis to add to a hypothesis, or to contribute to disproving it.
I am guessing now, too, that when multiple matches descend from a MRCA who is not my ancestor, but must be a descendant of of a common ancestor with me even further back in time, then all the lines should be roughly equal in average cM.
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