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X-DNA Advanced Advanced topics about X-Chromosome matching and anthropologic blocks based on SNPs and/or STRs.

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  #1  
Old 17th July 2018, 07:19 AM
Sem1953 Sem1953 is offline
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X Chromosome

I am wondering what a 7.7 cM autosomal match with a 195.93 X match means?
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Old 17th July 2018, 09:52 AM
georgian1950 georgian1950 is online now
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Quote:
Originally Posted by Sem1953 View Post
I am wondering what a 7.7 cM autosomal match with a 195.93 X match means?

GEDmatch? Family Finder?

What is the predicted relationship or generations to MRCA?


I would think that the size of the match on X would mean a common ancestor within a few generations. What are the genders of the two people being compared? Of course certain lines are not feasible for X-matching (a father does not pass an X to a son).

Just need more information to give an answer.

Jack
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Old 17th July 2018, 10:23 AM
Sem1953 Sem1953 is offline
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X Chromosome

Thanks for your reply. It is on Family Finder. My donor is female. The match is male. 20 shared segments, the largest is 7.7. Shows as 5th to remote cousins. He does not show up as a match to my donor's son.

My donor is on gedmatch, but did not find match there.

His listed surnames are all Spanish. I do not have any Spanish surnames in my family as far as I know

Thanks.

Last edited by Sem1953; 17th July 2018 at 10:27 AM.
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Old 17th July 2018, 11:13 AM
John McCoy John McCoy is offline
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If two kits show a complete match on the X chromosome (about 195 cM) on FTDNA, but the same two kits don't show an X match on GEDmatch, there is something wrong! For GEDmatch, be sure you are using the X One-to-One comparison tool, which seems to produce the most reliable results.

For the future, the best statistic for purposes of discussion, the number we want to see first, is usually the total shared cM for the autosomes (chromosomes 1-22), rather than the number of segments and/or the size of the largest matching segment.

One thing that goes wrong on GEDmatch, sometimes people who manage more than one kit on FTDNA upload the WRONG FTDNA KIT on GEDmatch and don't realize it. Ordinarily, any FTDNA matches you have who have also uploaded their FTDNA data to GEDmatch should also be found among your GEDmatch matches, and the segments should be very similar in location and size.
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Old 17th July 2018, 12:38 PM
Sem1953 Sem1953 is offline
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X Chromosome

Sorry, it is 20 cM total, with 7.7 the largest. My mistake, I put 20 segments. Apparently, my match did not upload to Gedmatch because he does not show up in my matches on that site.
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  #6  
Old 17th July 2018, 01:06 PM
Emona Emona is offline
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Family Finder does not count X-Chromosome segments when relationship is estimated.
In this unique case, X may be important, and the relationship may be closer. Something like half-2C1R?
This situation seems to be on the edge of statistically possible.

Have you tried to contact Mr. Match? You can invite him to gedmatch. It would be great to check your case there.
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Old 17th July 2018, 01:21 PM
Sem1953 Sem1953 is offline
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X Chromosome

Thanks, I will do that.
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  #8  
Old 17th July 2018, 01:35 PM
John McCoy John McCoy is offline
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I agree, it is extremely unusual to find a complete X match with such a small autosomal match. It should be possible, for a relationship perhaps as remote as 3rd cousins, but I've never run into a case like this. Please let us know if you are able to get any more information about the actual relationship!
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