A Segment-ology TIDBIT
I’d like to encourage all “Segmentologists” to periodically review the comments to my blog posts. I try to respond to every one of them and often go into more detail and/or provide suggestions for specific issues. If I may say so, there are often some more gems in the comments – including feedback from followers of this blog. I recently got a comment and elaborated on a post from over 7 years ago…
[22BK] Segment-ology: Review the Comments TIDBIT by Jim Bartlett 20221213
segment-ology 
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Maybe you can give me a little guidance. I have a young lady who knows who her birth mother is, but not her birth father, and her BM refuses to share the BF. A large number of her birth relatives have DNA profiles. I have matched them down to Gen #4. I have one stand out male donor who has a match of at least two areas on every chromosome except #16, for a total of 48 matches. Her BM also has at least two matches on every chromosome, with only one match on #21, for a total of 50 matches. Since the male donor is also a relatively close family member, how should I proceed from here?
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Don, If the stand out male donor matches your friend on almost every chromosome; and he alos matches your friend’s mother (BM) on almost every chromosome, then it is highly likely the stand out male donor is related to your friend on her BM side, and not much help on the BF side. Unless I didn’t understand your query. Jim
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I think I may getting the hang of this. On GedMatch, I did a One to Many search, and her BM has a total of 3568.6 cM, while the match to suspected BF was only 1125.8 cM and another suspected BF was only 302.1. And those are the two highest male matches. If I read your earlier message correctly, neither one are BF?
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Don, I think you are catching on, too. I recommend to you this website: https://dnapainter.com/tools/sharedcmv4 – this is the Shared cM project combined with a nifty tool by DNA Painter. Just plug in a total cM amount and it instantly tells you the probabililities. As you note 3500cM +/- will always be a parent/child relationship. 1125cM is almost always a 1C or a half AANN (Aunt,Uncle, Niece, Nephew) or a Great AANN – you are probably not dealing with a Great grandparent or Great grand child (two generations away in a direct line). You might want to noodle around the DNA website, they have several great tools there.
It is very unusual, in genetic genealogy, to find a birth parent with a 3500cM Match. Usually the top Matches are more distant. Although the 1125cM Matches is not the BF, it is very close… I’d be looking for the family Tree that the 1125 Match is in… Jim
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Thank you so much, you have helped to close the case. None of her matches are her BF.
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Hello Jim, I have a question that you probably can help with. I have someone searching for their BF. While they have 50 chromosome matches to their known BM, they also have 48 chromosome matches to a male. What are the chances that this is their BF? Thank’s Don
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Don, When you say “48 chromosome matches” do you mean a shared segment of 48 cM. Note that cM is the abbreviation for centiMorgan. Generally a parent/child match is about 3400cM – which much more than 48cM. 48cM, on average, is about a 3rd cousin. Please let me know if I’ve interpreted your question incorrectly. Jim
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Thank’s, will do more research
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Thanks for your response. Let me see if I can explain myself a little better. For maybe BF, on Chromosome #1, they have 3 segments that they match on, and the cM’s total 107.3. On Chr #2 the cM’s total 67.0 and on down the line for a total of 1133.2 when I combine all of the cM from all of the 21 cM reported matches. I appreciate you being patient with me, since I’m a very Old Dog learning new tricks. When I said 48 matches, I meant where there was a cM overlap.
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Don, If someone can reasonable separate their closest Matches to those on the maternal side and those on the paternal side. That is a great first step. All of the Matches on the paternal side must come *through* the bio-father (BF). If a number of them all agree on a Common Ancestor, that CA is almost certainly an Ancestor of the BF – say CA1. Idealy, what we want to do is find a second CA among another group of close Matches on the paternal side – say CA2. Then we research the descendants of CA1 and CA2 and look for a marriage (or relationship) between the two families – this marriage (or relationship) is highly probable to be the parents of the BF. We then try to get someone as close as we can to this line to take a DNA test and see if it shows a really high cM value. Hope this helps, Jim
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Thanks for your feedback;>j
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I always read the comments. I find that the discussions of the ideas and questions raised by the articles provide further clarification, or extend the ideas in useful ways.
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