using X DNA matches

Question

I enjoy going down the list of DNA matches on 23 and ME, and trying to pin down the paper trail to put them in the tree. A few days ago, 3 new males popped up, and I was quickly able to find out that they were 3rd cousins of mine thru the Wright/Sessions family of NC. All 3 were 2nd cousins of each other, and unaware of any of these relationships. It was fun! Then I noticed that one of them shared 40 cM on the X chromosome with me. I've never noted this before. Males with an X match? I looked it up.... the company says X matches are significant for females at 3 cM , and at 1 cM for males. We got this large 40 cM segment from our GGGM Eliza Jane Cromartie (Cromartie-12). The other two 3rd cousin males lost this X match on the way down, as they had two males in a row in their lines, which automatically deletes an X. Then I checked for other 23andME testers who had this segment, and found 3 right away, one sharing a paper trail back 9 generations to Sarah (Ransom) Sessions (1711-1788) (Ransom -370). I searched some more and found 14 others with this same X segment match. I know that the size of an X match does not correlate with the distance of the relationship, but it does point us in the right direction. Is there an X chromosome discussion group on wiki? Who would be our experts? I have read what Blaine Bettinger has to say about it.

Comments

I don’t know what you mean by “significance” of a match. AFAIK that is not a well-defined term in genetic genealogy.

 But 3cM is way too small to care about. It is the opposite: generally you need more cM in an X-match than in autosomal to make it worth investigating— unless you have already identified a relationship with the match, and that’s your situation. Did you check all of the lines from yourself and these matches to your common ancestors to ensure that no line went through two males consecutively?

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I am brand new at the X DNA game, so I was just quoting the testing company about "significance". The first thing I did was check the male/female lineage of the matches, I thought I made that clear. Going back in time, I am MFMFFFMF to Sarah Ransom, Chip Hollister is MFFMFFMF. The other two 3rd cousins who did not have the X DNA segment, despite being autosomally the same relationship to Sarah Ransom, were MFMMFFMF (disqualified by the MM) and MFFMFFMF, theoretically qualified, just not "lucky". Any answers to my 2 questions?

Answer 1

X DNA seems quite tricky but like magic when you find those large segments that fit the trees. I think the "experts" would be anyone who is actively trying to analyze X DNA to answer genetic genealogy questions. I rarely see folks trying to work with it, in part because the tools available on more of the platforms are pretty poor. If you do post some questions somewhere else, let me know as I am interested in the topic.

Comments

I am a slow learner. I uploaded my kit to ftdna years ago, but did not know about their having a chromosome browser until just now. Then I discovered that their browser allows us to "search for X- matches" !! That is something the other sites do not offer. I quickly found 4 more X matches (out of 7000 matches) and one is thru the same Sarah Ransom Sessions mentioned above, the other 3 are thru another X match that I had found before. Very powerful stuff!