Trying to understand FTDNA's X-matches

Genetic genealogy is the application of genetics to traditional genealogy. Genetic genealogy involves the use of genealogical DNA testing to determine the level and type of the genetic relationship between individuals.
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MarcuccioV
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Trying to understand FTDNA's X-matches

Post by MarcuccioV »

I'm trying to understand FTDNA's X-matches. I did the "chromosome browser" with several dozen (just a fraction of the total) of my "X-matches" (which are a small fraction of my total matches). 90% (or more) of them fall within the same range near the center of the chromosome. Many fall in the EXACT same range. Now most of the matches are female (XX/XY karyotype). I think only one was male (XY/XY karyotype). The cM ranges between 1-5.

Furthermore, only ONE of the matches shows any Italian heritage, and she matched in a totally different position. The X chromosome is the Italian one (my mother was the Italian). Now my research indicates my grandmother MAY have had some French or Swiss/German ancestry, but how far back and how much (if any) is unknown. The above matches show these ethnicities at times.

So is this just coincidence..? Or perhaps are they matching that minute bit of French/Swiss/German that I suspect..? It just seems off to me that such a vast majority of the X-matches lie on such a small part of the chromosome and only in a couple of cases not...
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Re: Trying to understand FTDNA's X-matches

Post by afecad »

You are using autosomal data from Ancestry, you may get mixed results and to be honest I have not found FTDNA X-matches to be of any use and/or are so distant.

Did you see any matches on Ancestry of Italian origin? I see lot's of matches, my Grandfather had 9 siblings who all married and had kids, as well great-granduncles and aunts who came over from Italy as well, had families. All of these show matches on Ancestry and 23andme.
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Re: Trying to understand FTDNA's X-matches

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afecad wrote: 08 Mar 2021, 16:44 You are using autosomal data from Ancestry, you may get mixed results and to be honest I have not found FTDNA X-matches to be of any use and/or are so distant.

Did you see any matches on Ancestry of Italian origin? I see lot's of matches, my Grandfather had 9 siblings who all married and had kids, as well great-granduncles and aunts who came over from Italy as well, had families. All of these show matches on Ancestry and 23andme.
Here is the bizarre thing: One of my Ancestry matches is very close (1st-2nd cousin, high cM match), 2nd only to my KNOWN first cousin, but higher than known 2nd-3rd cousins.

However, her only tree match is we have a 6GG in common (my father's & her mother's sides). Yet she has high Italian ethnicity and our shared matches are ALL Italian, with one of them having the same surname as my maternal tree. Her tree shows NO Italian surnames back 6 generations or more, but again, high Italian ethnicity.

That one STILL has my head spinning...
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MarcuccioV
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Re: Trying to understand FTDNA's X-matches

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So even if she were adopted, why the 6GG match on my father's NON-ITALIAN side is what makes me wonder. I suppose anything is possible. She seems to have no knowledge of her Italian ancestry, which is considerable (around 50%, same as me). All of our shared matches (ALL of them Italian) seem to fall in the 4th-6th cousin range for both of us.
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Re: Trying to understand FTDNA's X-matches

Post by afecad »

Ancestry is estimating based on cM of matching but is not accurate, for me it only list one 1st Cousin and it's actually my 1st cousin's Son and yet they grouped it under "1st Cousin" but also noted "1st-2nd".

23andme does a much better job of displaying DNA relatives, the same relative above is listed as "Father's side, First Cousin, Once Removed" which is 100% accurate. Some people did both Ancestry and 23andme, so they show up, but 23andme is more accurate and the fact it notes material and paternal is great.

Also keep in mind, Ancestry's family trees are often not accurate and many people tie connections to relatives that are not verified or have a good paper trail.
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Re: Trying to understand FTDNA's X-matches

Post by neseoopy »

I am baffled by the match described below. Please, can someone with a better understanding of the x-chromosome help me?

F and M are the father and mother, respectively, of Daughter 1 (D1) and Daughter 2 (D2).

F and his children have a fairly strong autosomal match (38 cM in one segment) with Cousin (C).

M and C have no autosomal or x match.

F and C have no x match.

From triangulation it is clear that the match between F and C is on F's father's side, not his mother's.

Yet, D1 and D2 both show x matches of the same 7.9 cM segment with C. How is this possible, since the x that F passed on to his children was from his mother?

Thanks a lot.
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Re: Trying to understand FTDNA's X-matches

Post by MarcuccioV »

neseoopy wrote: 22 Aug 2021, 09:55 I am baffled by the match described below. Please, can someone with a better understanding of the x-chromosome help me?

F and M are the father and mother, respectively, of Daughter 1 (D1) and Daughter 2 (D2).

F and his children have a fairly strong autosomal match (38 cM in one segment) with Cousin (C).

M and C have no autosomal or x match.

F and C have no x match.

From triangulation it is clear that the match between F and C is on F's father's side, not his mother's.

Yet, D1 and D2 both show x matches of the same 7.9 cM segment with C. How is this possible, since the x that F passed on to his children was from his mother?

Thanks a lot.
It took me a while to sort out your quandary, but I see your point of confusion.

Were all these people you mention (F, M, D1, D2, C) tested by the same matrix..? I ask as different companies get their info from different SNP's. 2 individuals tested by different matrices will share different results.

As an example, I'm currently in contact with a distant cousin found though GEDMATCH. I uploaded 2 different tests, Ancestry & 23&Me. My matches to this individual varied tremendously between the two matrices. Our match from my 23&Me test was 105cM over 21 segments; from my Ancestry test (far fewer SNP's compared) we only matched 5cM on 1 segment. That segment, however, is the same for both.

Therefore, if these people tested with different matrices and only uploaded to FTDNA, it's possible you have the same or similar situation in which M & C were not tested on the same SNP's, therefore no matches would be found.

I'm not certain this applies in your case or not, just sharing my experiences...
Mark

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