X-Chromosome Matching at Family Tree DNA

Just as they promised, and right on schedule, Family Tree DNA today announced X chromosome matching.  They have fully integrated X matching into their autosomal Family Finder product matching.  This will be rolling live today.  Happy New Year from Family Tree DNA!!!

In the article, X Marks the Spot, I showed the unique inheritance properties of the X chromosome.  In a nutshell, men only inherit one copy from their mother, because they inherit a Y from their father, but women get a copy from both parents.  Still, you don’t inherit parts of your X from all of your ancestors, so knowing your own X inheritance pattern can help immensely to rule out common genealogy lines when you match someone on the X.

In their informational rollout, Family Tree DNA provided the following information about their new features.

Here is the menu link to the Family Finder Matches menu.

x match 1

On the Family Finder Matches page, there is a filter to show only X-Matches.

x match 2

When you use the X-Match filter on a male Family Finder kit, you should get only matches from the maternal X-Chromosome.

x match 3

Next, like other Family Finder Matches you can expand the advanced bar for a match and click to add the match to the Compare in Chromosome Browser list.

x match 4

Matches are added to the Compare in Chromosome Browser list. You could go right to the Chromosome Browser by clicking on the compare arrow at this point.

x match 5

Next we can also go right to the Chromosome Browser.

x match 6

The Chromosome Browser also lets you filter the match list by X-Matches.

x match 7

Here are three immediate relatives. The first two share X-Chromosome DNA. The third (green) one does not.

x match 8

When we scroll down to the X at the bottom, we see that X-Matching is displayed for the first two but not the third.

x match 9

Moving to the Advance Matching page, X-Chromosome matches have also been integrated.

x match 10

X-Match is an option that can be checked alongside other types of testing.

x match 11



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254 thoughts on “X-Chromosome Matching at Family Tree DNA

  1. So just to clarify: all of my X matches will not be any of my paternal relatives. They will only be maternal matches? Then, is correct to say they will only be matches from my mother’s mother (maternal grandmother)?

  2. I just had a preliminary look. Only one of the matches I had considered interesting showed up there, but when I did a “common matches, in common with” for her, I got all my father’s people. I figured she matched on both of my sides, but I was kind of hoping this would show who else she matches specifically on my mother’s side. I obviously have work to do here.

    • I just checked with FTDNA to see if this was a bug or not. It’s not, but the idea of an X only ICW feature has now been passed on to the person who aggregates “cool ideas” that may one day become product features.

      • At FTDNA I have only one X match, and that person matches only on the X, nowhere else. I’m not sure what to make of it.

        • I have autosomal matches using gedmatch.com with no X matches. My guess is that I match the male lines of the autosomal dna.

  3. Dear Roberta,

    Great post and exciting news!

    If your ancestral tree is in http://www.wikitree.com then WikiTree automatically shows which of your ancestors could have contributed to your X chromosome. Here are the ancestors who could have contributed to my paternal aunt’s X chromosome http://www.wikitree.com/treewidget/Roberts-7123/89#X

    WikiTree makes it very easy to share one’s X-DNA chart with their X-DNA matches.

    Happy New Year!

    Best regards, Peter


  4. Another thing. I am happy to learn of this announcement from your blog, which I see anyway, but I don’t understand why FTDNA doesn’t send out a blast with this kind of announcement to all their customers – or at least their GAP administrators.

    • They do. That’s how I knew when to release this. They post it on their forum and on the GAP page, they indicated they were going to have all of the feature announcements there as well. I think they also post it on their Facebook page. Beyond that, I don’t now. If finally quit sending bulk e-mails to project members with very few exceptions because I got complaints from people who didn’t want informational e-mails and because my address kept getting blacklisted on servers as a spammer.

  5. Very cool that it is up. THank you for a heads up! My transfer from Ancestry is not included in the X matching. Interesting. Busy looking at the parents’ matches!

  6. I don’t think it’s available everywhere. I signed on and it’s not showing in the drop down box for Family Finder matches.

  7. Hi Roberta

    I am absolutely delighted that Family Tree DNA now has this X Chromosome Matching feature!!!

    Karen and some other DNA cousins and I started using the Charting Companion Program from http://progenygenealogy.com/ to do beautiful fan charts with our X chromosome ancestors marked in pink and blue so that we can easily spot and compare x chromosome ancestors. Charting Companion makes several different types of X Chromosome Ancestor Charts but I like the fan chart the best. I was fascinated by your earlier blog on X chromosome ancestors and am still very enthusiastic about X chromosome genealogy research. Before I found a program that had the X Chromosome ancestor chart formatting feature, I used Microsoft Paint to try to color in the appropriate spaces on my ancestor fan chart produced in another program in order to figure out X Chromosome matches as you suggested. Using Charting Companion to quickly produce the charts from my PAF data base was easy as pie. Karen used Charting Companion with her Family Tree Maker data base. It works with a variety of formats including GEDcoms. Now all I have to do is wait for enough X chromosome descendants of my X chromosome ancestors to test so that we will be able to figure out how we are related.

    Charting Companion also makes a variety of other genealogy charts which can be blown up into decorative posters. Karen and I both made charts for various family members for Christmas. I would have bought Charting Companion it because of the time it saved me in coloring in X chromosome ancestor charts alone, but the decorative charts were an added feature that I really enjoyed using. Now, how can I get more of the unknown descendants of my X chromosome ancestors to take the Family Finder Test???

    • I just had an inkling of how the X Chromosome worked until Aleda told me about Charting Companions through progenygeneaology.com. So for a very cheap price I went online and ordered the program and downloaded it. I am not very computer literate at the best of times. I could not understand when Aleda told me how to color the X Chromosome Chart with “Paint”. As soon as I downloaded the Charting Companions Program and made myself an X Chromosome Chart, it appeared immediately by using my family tree program to get the needed info.
      It was one of those “A HA!” moments. There was my wonderful chart in blue and pink and for the first time I could understand all the things I’d been reading on Roberta’s blogs and what Aleda had been telling me about. It became crystal clear to me in that instant as to how the X Chromosome works. The program is wonderful when someone like me can use it so easily.


  8. Hi! Thanks for the info! I have two X-questions:
    1. Is my X chromosome (as a male) a mix of my mothers two X’es?
    2. For females, why is there only a single raw file to download for the X chromosome? Is that one of the X’es or a mix?

  9. Can’t wait to have a look at this feature. Unfortunately, as of 5:00 pm CST, the FTDNA site is down due to maintenance.

  10. Pingback: FTDNA Adds X Chromosome Matching | Ups and Downs of Family History

  11. Roberta,

    Thank you for this post! This is a test to see if I’m beginning to understand matching. I have a scenario. I’ll explain it to you and you can tell me if I’m on base or way off base.

    MM is a man who matches me through Family Finder. I believe I know our common surname, but I don’t know our common ancestor. If we match through the surname BLUE, the one I believe we have in common, then he matches me somewhere on my father’s side. If he matches me on my father’s side, and ONLY on an ancestor on my father’s side, then is there any way he would match me on my X-chromosome? I am thinking not.


        • Just because he could share an X match with you doesn’t mean that he does. You match autosomally, not on the X. What this is good for is IF you match on the X, there is a special inheritance pattern for the X chromosome, so you can eliminate about half, sometimes more, of your genealogy lines off the bat.

      • I have his pedigree chart back to his BLUE ancestor. Using the charts in your X Marks the Spot article, I see why he and I would not have an X match (with the assumption that we are related via the line, and only the line, that I surmise). Filling in the charts for both of us helped me to understand X-matching! Now to move on to some people who I DO have X-Matches with. THIS is very exciting!

  12. I have looked at the X match in FTDNA for my daughter and her great-uncle. Only my daughter has matches. Are they only doing x matches for females? All of her matches except one also seem to be female. She was tested at 23andme and uploaded to FTDNA whereas he was tested at FTDNA and his results only came through yesterday. Do you think that’s why he has no X matches yet and maybe they will come up in a day or two? By the way your cousin Michael comes up on my daughter’s matches. I think it is probably the Acadian connection. Her GG-Grandmother was a fully french Louisianian Cajun with the surname of Boudreaux.

    Thanks for the heads up on this.

  13. Roberta, I have a man and a women who match me both on the same segments of the X-chromosome, the same segments of Chromosome 8 (not exact, but their matches on that Chromosome overlap each other), and are related in the Matrix Match Tool. This looks like a home run, but what kind of home run? In layman’s terms, how may they be related to each other and to me?

    • I contacted FTDNA about my small number of X matches and the fact most of those matches were very small (< 2 cM). Here was their response:

      Hello Mr. —
      Thank you for your email. It is not unusual to have very little or no X matches, and for the total shared X chromosome DNA to be very small. The X chromosome drops off very quickly in the inheritance process.

      Morgan H
      Office Support Assistant
      Data Assurance
      Family Tree DNA

      Not an incredibly detailed or satisfying response, but there you have it.

      • Hi again Roberta,
        OK – I seem to have found an issue here. I had my mother and myself tested with Family Finder. As her son, I inherit her xDNA. However, when I look at her xDNA matches, she has 31 matches and I have two – namely my mom and her sister. I thought it might be that perhaps I didn’t get some of her atDNA matches and so they might not show up at all. But that is not the case. I checked her top two matches, and I also have them as atDNA matches. They don’t however show up as xDNA matches to me. My only guess is that I get a compressed version of my mother’s xDNA (since she has an XX while I have an XY) that doesn’t cross the threshold for a match. I noticed that the kits I manage have the men with many fewer xDNA matches than the women.

  14. I have had problems getting it to work using chrome. It keeps trying to load. On internet explorer it works great. I have had X matches on most of my autosomal matches,

  15. question – I have 5 PF matches and zero X matches, is it safe to say that these 5 PF are all on my paternal side?

  16. Does the maternal X chromosome have a little tag on it to identify it as such?

    I found 6 x matches at FTDNA and 2 on 23andme. I am a male. You are saying the FTDNA X match came from one of my female ancestor/testers?

    Steve in Oro Valley

  17. I have only one (1) good X match(1845 and 1853 Arkansas) at FTDNA out of 700 cousins. She also appears as an X match at 23andme (over 1000 cousins). A few others look promising but they do not have a family tree or surnames . I have a much greater number of autosomal matches at both places which are pretty obivous….

    She jumped right out, though, as she and I had a common gggrandmother back in Arkansas. Almost no doubt about it. Of course, the woman had 18 children, Ever hear of Russelville, Arkansas?

    By the way, the name Estes shows up occasionally among the FF surnames. I live in an Estes built home here in Oro Valley, Arizona.

    Steve in Oro Valley

  18. One of my X matches only shares a ~1 cM segment on the X chromosome; and the matches we share in common (all icw each other, etc.) don’t have that segment. This person is being marked as an X match on my list on the basis of that segment, but it seems just as likely to me that that is an IBS segment. Also, they’re pretty sure, on the basis of the icw matches, that the match is in their direct paternal line. Is there anything I’m missing?

  19. You must be so tired of answering all these questions, so if you can bear just one more…I have 60 X matches. Lots of segments in the 2cM or 3cM range. Should these be discounted as just noise then? Should we just concentrate on those in the 5 plus range? Many thanks.

    • I wouldn’t just discount them. I would however, concentrate on the larger ones first. One thing we know is that the X just doesn’t follow the rules very well. Some people carry almost nothing of their great-grandparents X and some carry it almost intact. So it’s less reliably predictive is what I would say – but in both directions.

  20. One of my four X-matches (out of 289 total FF matches) is also an autosomal match with my two closest cousins on my father’s side. Based on my extensive genealogical research, I do not see how this can possibly be correct, if the X-matches are only on my mother’s side. Am I missing something?

    • No, you’re not missing anything. But perhaps they match this person on their X through a different. Follow the X of your cousins to see if they can match this person on the X on your common line.

  21. The browser does not show any overlapping X-segments between my two paternal cousins and my maternal X-match. I should add that the length of my X-match is just 1.94 cM. This sure looks like an anomaly.

  22. Roberta thanks so much for keeping us informed. I don’t know what I would do without your timely and informative emails. I do have a question however. Does Family Tree DNA ever send these announcements to people like me who have had DNA tests and are in their database? As I said, I appreciate it that you report but why don’t they send it to each of their clients as well? Betty

    • Hi Betty,

      I can’t answer for them, and I would suggest you ask them. My suspicion is that they would get hundreds of complaints. That’s why I quit sending e-mails about things to project groups, along with constantly having my e-mail blacklisted for spam.


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  24. Roberta, I re-read my latest question and realized it was most certainly too broad, so I thought I’d try another one. The way you described X-matching in X Marks the Spot post was very helpful. I printed out one of the female fan charts and filled it in.

    I understand that my X-matches can only be related in the highlighted areas on my chart. But can they also ONLY be X-match related to me through their ancestors on the highlighted areas of their charts? Or could they be X-match related to me through any of their ancestors.


  25. Pingback: What does shared X DNA really mean? | Kitty Cooper's Blog

  26. Roberta – thanks so much for your work on this. One question, how do you interpret xDNA overlap on the chromosome browser? For the other chromosomes, if I have two common cousins and they visually overlap on the chromosome browser, I consider that a solid match. With the xDNA though, I have a cluster of 7 folks who have about the same 1.5 to 2.5cM segment on the xDNA. They however don’t appear to be common matches with each other and I don’t see any overlap in the other chromosomes. There are only 11 xDNA matches, so 7 is the majority and it seems odd they all overlap. Or should I just discard anything less than 3cM unless there’s some other supporting evidence?

    • I understand that the chromosome browser size of segments is a bit overstated and that you really need to rely on the download to see the actual size of the overlap. I would be skeptical, especially on female/female segments less than 3 – but I wouldn’t discard them.

  27. I have a questions about X-Matches. You say that a male who tests at Family Finder can eliminate all his maternal lines using it. What can a female who tests eliminate?

    Here is a sample line (Jane Smith) starting with Jane’s parents:

    L Smith
    K Smith
    A Thomas
    FATHER – J. Smith
    B Jones
    A Jones
    A King

    C Brown
    B Brown
    A Harrison
    MOTHER – A Brown
    B Davis
    A Davis
    A Fisher

    Let’s say that Charlie Chapman shows up on Jane’s list of X-Matches, does that mean he does NOT match her on one of her father’s lines but on one of her mother’s lines?
    What if Cindy Chapman shows up on her list of X-Matches?

    What if William Winkler does NOT show up as one of Jane’s X-Matches. Does that mean he does not connect to her through any of her mother’s lines but on one of her father’s lines. OR could he connect to her through her grandfather B. Brown’s line? Would it be the same answer if Wilma Winkler was her match?

    Thank you, Carol

  28. Sorry. I had these people set up nicely and the margins were eliminated.

    Here is my letter again:

    I have a questions about X-Matches. You say that a male who tests at Family Finder can eliminate all his maternal lines using it. What can a female who tests eliminate?

    Here is a sample line (Jane Smith) starting with Jane’s parents


    A KING





    At least I THINK that’s what I had. I added the names, so you could tell me which lines would be eliminated and/or which lines would match.

    Let’s say that Charlie Chapman shows up on Jane’s list of X-Matches, does that mean he does NOT match her on one of her father’s lines but on one of her mother’s lines?
    What if Cindy Chapman shows up on her list of X-Matches?

    What if William Winkler does NOT show up as one of Jane’s X-Matches. Does that mean he does not connect to her through any of her mother’s lines but on one of her father’s lines. OR could he connect to her through her grandfather B. Brown’s line? Would it be the same answer if Wilma Winkler was her match?

    Thank you, again, Carol

  29. Hi Roberta
    Wouldn’t it be easier for people who already have their ancestry in PAF, Family Tree Maker, Roots Magic or Legacy files to buy the Charting Companion Program for $50 or less and produce Ancestral Fan Charts or some other format of chart that automatically marks all of their X chromosome ancestors in pink or blue? I spent countless hours trying to mark my X chromosome ancestors on a computer generated fan charts using Microsoft Paint to color in the blocks for my X-chromosome ancestors. Once I found out about Charting Companion, I bought it. It takes minutes to make a chart with the ancestors colored in correctly, Just go to this address to look at the product:
    As soon as I find a new ancestor, I can generate another chart using charting companion. I have found at least two ancestors since I bought the program a couple of months ago although I don’t remember whether they were X chromosome ancestors or not. I knew how to figure out who were my x chromosome ancestors before I bough Charting Companion, but the people who don’t know would find out immediately and it might help them understand the principles for determining who are their X chromosome ancestors.

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  31. Hi Roberta, and thank you for all of the information. I am a newcomer to DNA testing and was quite surprised when ftDNA matched me to a lady in Montreal that was an astounding DNA match. Now that they have added the X chromosome information it gets even wilder. The lady in question was a foundling – left on a doorstep – so has no idea who her biological parents were. On the X chromosome we share 170.13 cM and 16592 SNPs. The autosomal results are a total of 961.60 cM shared with a largest block of 99.03. We do not match on mtDNA, so would I be correct in thinking our match would be on my maternal grandfather’s side?

    • Hi Glenn,

      The fact that your mtdna does not match tells you that it’s not the direct maternal matrilineal line – but it could be any other X candidate. At least that one line is ruled out for you.

  32. Roberta, We have a grandmother, daughter, granddaughter(autosomal matches)
    that all match my father, my sister, and myself. They all stack on chromosome 22 and it was believed that this match was through my father’s paternal grandmother’s side. They all just came in as X matches to my sister and myself. Not my dad. Am I correct in my thinking (backed up by fan chart) that this match cannot possibly be through the line we first thought? (my dad’s paternal grandmother). Also, the three ladies are all located in different areas of the x chromosome. None of them stack with each other. Why is that?

    • Correct, it cannot be from your father’s anything. He didn’t get an X from his father. It’s possible that you are dealing with more than one line here. The fact that they don’t overlap only means they didn’t get the same segment piece.

  33. Roberta, I just discovered a message on GEDMatch’s home page.

    Autosomal raw DNA
    NOTICE: Apparently, FTDNA has changed the format of their raw DNA data files, and they are no longer compatible with GEDmatch upload software. Please contact FTDNA for more information.

    Perhaps it is the addition of this data in the raw files. Have you heard of this yet?

  34. Roberta, the work you have presented here and in your X Marks the Spot post have really helped me to understand X Matching, but I am still fuzzy on one point. If someone is NOT an X-Match to me, does that mean he or she is NOT my relative on one of my X-Chromosome lines and can only be a relative on the non-X lines (or the “white” areas on the pie charts)?

  35. Roberta,
    Thank you very much for this blog (just discovered it). I’m thinking of buying the software mentioned earlier in a post, and wonder if it might help me solve a question such as this one:

    Background: my maternal grandparents are first cousins
    My maternal first cousin and I tested autosomal, ydna (him), and mtdna. My brother also tested ydna. Brother and cousin do not match ydna haplogroup. Cousin mtdna does not match my mtdna haplotype.

    Cousin’s father and my mother were brother and sister.

    As expected, cousin and I turned up as close relatives on autosomal. Unexpectedly, we are also x-matches with 50 shared segments. It doesn’t look very significant on the chromosome browser. Am I right?

    Where does our x-match come from? If I read correctly, it could come from either his mother or his father. I’m guessing ydna does not factor in here at all…..

    I think I will buy the program, but your response would be greatly appreciated. Thanks!

  36. I am seeking the surname of my paternal great grandmother. What test will help me accomplish this?

    • That is not a question with an easy answer. Even with DNA testing, it will take work on your part. Your best bet is the autosomal test – Family Finder at Family Tree DNA. You will want to test the person alive generationally the closest to that person.

  37. Hi Roberta,

    Hoping you can clarify for me. I have been searching for the parents of my great-grandmother on my paternal side. I managed to connect on FTDNA with 3 others who I matched on a 3rd cousin level; one male and 2 female. Comparing our X-chromosome I am showing the following: 1 ; 6.15,4.27 snp 1025, 500 2: 6.81, 7.19 snp 550,592 3 (male match) : 40.29 , 3725 ….The male match his mother was a direct line descendant from the line I’m looking for. Would I be safe to say that this is the proper line?

  38. There is a question regarding the birth mother of my G Grandfather. His sister’s descendant is an X chromosome match with me. Does this mean that my G Grandfather and his sister share the same birth mother? If so… Happy Days!!….

  39. This is a fascinating thread. I also have a question. My search is to identify my unknown maternal grandfather. All of my FTDNA X-matches (5) are known maternal relatives. I have found one 23andme match who matches one of my brothers and me on X for 33 cM; she is also an autosomal 6 cM match on chromosome 7. She is otherwise unknown to me (and apparently somewhat reluctant to connect, although she shared 23andme genomes). This person does not X-match a female half-cousin on my mom’s side. Does such a large match that doesn’t match my maternal half cousin suggest a good likelihood that she is related via my mystery maternal grandfather? Thanks!


    • No, I don’t think you can make that leap of faith. They may simply have not inherited some of the same X that you did. The X is more prone to an “all or nothing” type of inheritance than the other autosomes.

  40. I have had a couple of matches to say we don’t match on a particular person when it seems so obvious that we do match because of the person or persons. How much should one read into this chrome browser as gospel truth??

  41. Why would I have X-chromosome matches that my mother does not? Only 1 of the 4 matches, match her? Does this mean they are on my father’s maternal line?

      • I also should have mentioned I am male. I am very new to this, but I was told men only inherit X-chromosome from their maternal line since they receive Y-chromosome from their paternal line. Sorry, but I’m a bit confused.

          • robertajestes thank you for taking the time to reply and I apologize for my continued confusion. It seems like from your previous comment that you are confirming that because I am male I only inherit my X-chromosome from my mother. With that said, why is it that in FamilyTreeDNA’s Family Finder that I have 5 x-matches, however 4 of them are not matches with my mother? I don’t understand how I, as a male, could have an x-match which is not shared with my mother. Thank you again for your assistance.

          • No wonder you’re confused. You shouldn’t have any matches that don’t also match your mother. There have been X matching issues at FTDNA. Specifically, your mother’s may not have read well, and yours did. I can’t say what happened, but do rest assured that your X matches cannot come through your father. You can contact Family Tree DNA to report the issue.

          • Thank you! So either way, if my test read it and hers did not, because they are on my X-chromosome (x-match) they are on my maternal line.

            On a side note, it is truly a great thing you do for the researching public volunteering to answer these perplexing questions. Thank you for taking the time and effort to help others.

    • Not the Y, since it doesn’t combine autosomally. If you match someone other than the X, and you also match on the X, they show you as an X match – so yes, it would be included in the totals. However, if you only match on the X or not enough on the other chromosomes to be over the match threshold, then you won’t show the X amount because you’re not considered a match.

      • Thanks Roberta,
        I was not sure how the matrix was implemented- I am guessing that it clumps qualified segment matches together that contain the same allele value.

        Just a guess.

          • Thanks,
            The way I use the matrix is I only input matches that meet the length/overlap chromosome criteria. The FTDNA matrix will eliminate the ones that are not visible to each other. Does this visibility consider homogeneous allele grouping.in addition to the segmnet qulification you mentioned?

          • I guess what I am really asking is does the matrix address the issue of the the chromosome Browser Superimposing paternal and maternal chromosomes over each other – via allele grouping.

          • Thanks, So it sounds like homogenous allele grouping is not a visibility factor. I guess I need to look at phasing in more detail.

  42. Hi Roberta,

    I got an EMAIL last night – with the following comment..

    “This is useful when X matches show up besides the autosomal matches: you know that the X was inherited over a line with a maximum of one male in succession. If the X match is noticeably longer than the autosomal segments it is more likely that one or more males passed it on”

    Is this accurate?

      • Thanks for the reply. I am in fog on the statement aw well.

        I have rethought all my previous comments on the FTDNA Matrix – seems I had an over complicated concept which was not correct – your answer “It’s a match/no match criteria” -now makes perfect sense, just took me a while to figure it out. Thanks for for your patience in addressing all my questions.

  43. Hi Roberta, I still have only 6 X matches out of my 1156 matches. Only 2 of those X matches show up on the 5+ cm ranges, and then they both fall away at the 10+ cm range. What should I make of this ? That I have no reliable X matches, or that they are just further generations back ?

    • If you’re talking about at Family Tree DNA, remember your X match will only show IF you have another autosomal match too. So you may have X matches that don’t qualify because there is no corresponding autosomal. The X tends to be inherited in large chunks, sometimes almost entirely intact, so your X matches could be further back or on a side that hasn’t tested yet – or in people who don’t match you autosomally too.

  44. My mum has a known 3rd cousin on her paternal line (they have the same surname) but they are showing as an X match on FTDNA. The cousin and my mum share a total of 119.52 cM with a largest single block of 24.07 cM, and on the X chromosome they share a small block of 1.71 cM. I’m tempted to think that they may be related on more than one family line, especially since the autosomal match is much larger than what we would expect for 3rd cousins, but I realize this could just be a DNA fluke. Your thoughts would be much appreciated.

      • Thanks Roberta. I have commented on your article about ancient DNA kits at Gedmatch and the results of comparing my families kits against the Native American, Anzick. This shows that the X match that I referred to above could go back many many generations – but it’s there.

  45. Just when I thought I understood…bingo—confusion. I have a match on Gedmatch. This woman matches me, both my daughters, and one of my daughter’s sons in an autosomal comparison. The autosomal matches are all >14 cms. This woman does not match anyone on my father’s side of my family. She also does not match my wife (my daughters’ mother) either through an autosomal comparion or an X-DNA comparison. This woman also does match both my daughters on an X-DNA comparison (cms for both is 9.8.) The woman does not match me on X-DNA. How is it possible to have a situation where my daughters both match a woman through X-DNA when neither their mother nor their father match that person through X-DNA?

        • Ok, there are a couple of possibilities, none of them good ones. The first is that the DNA just happens to transition in the right location for part of a segment from the Mom to butt up against a piece from the Dad and the two together looks like a match to another person. This is known as a false positive. The other possibility is that mismatches are being “smoothed” and they are really mismatches and not read errors. This is not terribly likely, but you can affect that by increasing the two final numbers to be equal to the SNP count you’re looking at. So if you’re looking at 500SNPs, then 5cM, then the next two numbers should also be set to 500 which doesn’t allow any errors in that 500 segments. The third possibility is that GedMatch is having some sort of issue. I have found matching inconsistencies in matches to the Anzick data and then secondly, in repeated queries to other non-ancient kits. The net-net of this is that you’re right, the child can’t match what the parents don’t. If this was at a vendor, it would be possible that the total segment matching threshold was interfering, but at GedMatch, that’s not an issue.

  46. And this would apply in all cases? The case I described was not the only situation I found like this. In an earlier case the match was only at 7.1cm for the X-DNA and explained to me on the Gedmatch FB forum as simply a random match. It involved a totally different woman who does not match at all with the woman I gave you in the above case. In the other case the woman, her son and her grandson all matched me, my daughter and her son autosomally. The woman matched my daughter on X-DNA but did not match me nor my wife on X-DNA or autosomally in my wife’s case. I just find it odd that this sort of error would be so normal. And if it is, what value can we take from any match when a 9.8cm match is a fluke or some sort of distortion? I though a cm match of 10 was supposed to represent a 99% chance of an IBD match.

    “This is not terribly likely, but you can affect that by increasing the two final numbers to be equal to the SNP count you’re looking at. So if you’re looking at 500SNPs, then 5cM, then the next two numbers should also be set to 500 which doesn’t allow any errors in that 500 segments.”

    Excuse my ignorance but I really do not know what that means.

    • The challenge is that there aren’t any absolute answers and we can only go by what is statistically expected in certain circumstances. The instructions were for the settings in the GedMatch 1 to 1 comparison values.

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