That Unruly X….Chromosome That Is


Something is wrong with the X chromosome.  More specifically, something is amiss with trying to use it, the way we normally use recombinant chromosomes for genealogy.  In short, there’s a problem.

If you don’t understand how the X chromosome recombines and is passed from generation to generation, now would be a good time to read my article, “X Marks the Spot” about how this works.  You’ll need this basic information to understand what I’m about to discuss.

The first hint of this “problem” is apparent in Jim Owston’s “Phasing the X Chromosome” article.  Jim’s interest in phasing his X, or figuring out where it came from genealogically, was spurred by his lack of X matches with his brothers.  This is noteworthy, because men don’t inherit any X from their father, so Jim’s failure to share much of his X with his brothers meant that he had inherited most of his X from just one of his mother’s parents, and his brothers inherited theirs from the other parent.  Utilizing cousins, Jim was able to further phase his X, meaning to attribute portions to the various grandparents from whence it came.  After doing this work, Jim said the following”

“Since I can only confirm the originating grandparent of 51% my X-DNA, I tend to believe (but cannot confirm at the present) that my X-chromosome may be an exact copy of my mother’s inherited X from her mother. If this is the case, I would not have inherited any X-DNA from my grandfather. This would also indicate that my brother Chuck’s X-DNA is 97% from our grandfather and only 3% from our grandmother. My brother John would then have 77% of his X-DNA from our grandfather and 23% from our grandmother.”

As a genetic genealogist, at the time Jim wrote this piece, I was most interested in the fact that he had phased or attributed the pieces of the X to specific ancestors and the process he used to do that.  I found the very skewed inheritance “interesting” but basically attributed it to an anomaly.  It now appears that this is not an anomaly.  It was, instead the tip of the iceberg and we didn’t recognize it as such.  Let’s look at what we would normally expect.


The X chromosome does recombine when it can, or at least has the capacity to do so.  This means that a female who receives an X from both her father and mother receives a recombined X from her mother, but receives an X that is not recombined from her father.  That is because her father only receives one X, from his mother, so he has nothing to recombine with.  In the mother, the X recombines “in the normal way” meaning that parts of both her mother’s and her father’s X are given to her children, or at least that opportunity exists.  If you’re beginning to see some “weasel words” here or “hedge betting,” that’s because we’ve discovered that things aren’t always what they seem or could be.

The 50% Rule

In the statistical world of DNA, on the average, we believe that each generation receives roughly half of the DNA of the generations before them.  We know that each child absolutely receives 50% of the DNA of both parents, but how the grandparents DNA is divided up into that 50% that goes to each offspring differs.  It may not be 50%.  I am in the process of doing a generational inheritance study, which I will publish soon, which discusses this as a whole.

However, let’s use the 50% rule here, because it’s all we have and it’s what we’ve been working with forever.

In a normal autosomal, meaning non-X, situation, every generation provides to the current generation the following approximate % of DNA:

Autosomal % chart

Please note Blaine Bettinger’s X maternal inheritance chart percentages from his “More X-Chromosome Charts” article, and used with his kind permission in the X Marks the Spot article.

Blaine's maternal X %

I’m enlarging the inheritance percentage portion so you can see it better.

Blaine's maternal X % cropped

Taking a look at these percentages, it becomes evident that we cannot utilize the normal predictive methods of saying that if we share a certain percentage of DNA with an individual, then we are most likely a specific relationship.  This is because the percentage of X chromosome inherited varies based on the inheritance path, since men don’t receive an X from their fathers.  Not only does this mean that you receive no X from many ancestors, you receive a different percentage of the X from your maternal grandmother, 25%, because your mother inherited an X from both of her parents, versus from your paternal grandmother, 50%, because your father inherited an X from only his mother.

The Genetic Kinship chart, below, from the ISOGG wiki, is the “Bible” that we use in terms of estimating relationships.  It doesn’t work for the X.

Mapping cousin chart

Let’s look at the normal autosomal inheritance model as compared to the maternal X chart fan chart percentages, above, and similar calculations for the paternal side.  Remember, the Maternal Only column applies only to men, because in the very first generation, men’s and women’s inheritance percentages diverge.  Men receive 100% of their X from their mothers, while women receive 50% from each parent.

Generational X %s

Recombination – The Next Problem

The genetic genealogy community has been hounding Family Tree DNA incessantly to add the X chromosome matching into their Family Finder matching calculations.

On January 2, 2014, they did exactly that.  What’s that old saying, “Be careful what you ask for….”  Well, we got it, but “it” doesn’t seem to be providing us with exactly what we expected.

First, there were many reports of women having many more matches than men.  That’s to be expected at some level because women have so many more ancestors in the “mix,” especially when matching other women.

23andMe takes this unique mixture into consideration, or at least attempts to compensate for it at some level.  I’m not sure if this is a good or bad thing or if it’s useful, truthfully.  While their normal autosomal SNP matching threshold is 7cM and 700 matching SNPs within that segment, for X, their thresholds are:

  • Male matched to male – 1cM/200 SNPs
  • Male matched to female – 6cM/600 SNPs
  • Female matched to female – 6cM/1200 SNPs

Family Tree DNA does not use the X exclusively for matching.  This means that if you match someone utilizing their normal autosomal matching criteria of approximately 7.7cM and 500 SNPs, and you match them on the X chromosome, they will report your X as matching.  If you don’t match someone on any chromosome except the X, you will not be reported as a match.

The X matching criteria at Family Tree DNA is:

  • 1cM/500 SNPs

However, matching isn’t all of the story.

The X appears to not recombine normally.  By normally, I don’t mean something is medically wrong, I mean that it’s not what we are expecting to see in terms of the 50% rule.  In essence, we would expect to see approximately half of the X of each parent, grandfather and grandmother, passed on to the child from the mother in the maternal line where recombination is a possibility.  That appears to not be happening reliably.  Not only is this not happening in the nice neat 50% number, the X chromosome seems to be often not recombining at all.  If you think the percentages in the chart above threw a monkey wrench into genetic genealogy predictions, this information, if it holds up in a much larger test, in essence throws our predictive capability, at least as we know it today, out the window.

The X Doesn’t Recombine as Expected

In my generational study, I noticed that the X seemed not to be recombining.  Then I remembered something that Matt Dexter said at the Family Tree DNA Conference in November 2013 in Houston.  Matt has the benefit of having a full 3 generation pedigree chart where everyone has been tested, and he has 5 children, so he can clearly see who got the DNA from which of their grandparents.

I contacted Matt, and he provided me with his X chromosomal information about his family, giving me permission to share it with you.  I have taken the liberty of reformatting it in a spreadsheet so that we can view various aspects of this data.

Dexter table

First, note that I have sorted these by grandchild.  There are two females, who have the opportunity to inherit from 3 grandparents.  The females inherited one copy of the X from their mother, who had two copies herself, and one copy of the X from her father who only had his mother’s copy.  Therefore, the paternal grandfather is listed above, but with the note “cannot inherit.”  This distinguishes this event from the circumstance with Grandson 1 where he could inherit some part of his maternal grandfather’s X, but did not.

For the three grandsons, I have listed all 4 grandparents and noted the paternal grandmother and grandfather as “cannot inherit.”  This is of course because the grandsons don’t inherit an X from their father.  Instead they inherit the Y, which is what makes them male.

According to the Rule of 50%, each child should receive approximately half of the DNA of each maternal grandparent that they can inherit from.  I added the columns, % Inherited cM and % Inherited SNP to illustrate whether or not this number comes close to the 50% we would expect.  The child MUST have a complete X chromosome which is comprised of 18092 SNPs and is 195.93cM in length, barring anomalies like read errors and such, which do periodically occur.  In these columns, 1=100%, so in the Granddaughter 1 column of % Inherited cM, we see 85% for the maternal grandfather and about 15% for the maternal grandmother.  That is hardly 50-50, and worse yet, it’s no place close to 50%.

Granddaughter 1 and 2 must inherit their paternal grandmother’s X intact, because there is nothing to recombine with.

Granddaughter 2 inherited even more unevenly, with about 90% and 10%, but in favor of the other grandparent.  So, statistically speaking, it’s about 50% for each grandparent between the two grandchildren, but it is widely variant when looking at them individually.

Grandson 1, as mentioned, inherited his entire X from his maternal grandmother with absolutely no recombination.

Grandsons 2 and 3 fall much closer to the expected 50%.

The problem for most of us is that you need 3 or 4 consecutive generations to really see this happening, and most of us simply don’t have data that deep or robust.

A recent discussion on the DNA Genealogy Rootsweb mailing list revealed several more of these documented occurrences, among them, two separate examples where the X chromosome was unrecombined for 4 generations.

Robert Paine, a long-time genetic genealogy contributor and project administrator reported that in his family medical/history project, at 23andMe, 25% of his participants show no recombination on the X chromosome.  That’s a staggering percentage.  His project consists of  21 people in with 2 blood lines tested 5 generations deep and 2 bloodlines tested at 4 generations

One woman’s X matches her great-great-grandmother’s X exactly.  That’s 4 separate inheritance events in a row where the X was not recombined at all.

The graphic below, provided by Robert,  shows the chromosome browser at 23andMe where you can see the X matches exactly for all three participants being compared.

The screen shot is of the gg-granddaughter Evelyn being compared to her gg-grandmother, Shevy, Evelyn’s g-grandfather Rich and Evelyn’s grandmother Cyndi. 23andme only lets you compare 3 individuals at a time so Robert did not include Evelyn’s mother Shay, who is an exact match with Evelyn.

Paine X

Where Are We?

So what does this mean to genetic genealogy?  It certainly does not mean we should throw the baby out with the bath water.  What it is, is an iceberg warning that there is more lurking beneath the surface.  What and how big?  I can’t tell you.  I simply don’t know.

Here’s what I can tell you.

  • The X chromosome matching can tell you that you do share a common ancestor someplace back in time.
  • The amount of DNA shared is not a reliable predictor of how long ago you shared that ancestor.
  • The amount of DNA shared cannot predict your relationship with your match.  In fact, even a very large match can be many generations removed.
  • The absence of an X match, even with someone closely related whom you should match does not disprove a descendant relationship/common ancestor.
  • The X appears to not recombine at a higher rate than previously thought, the previous expectation being that this would almost never happen.
  • The X, when it does recombine appears to do so in a manner not governed by the 50% rule.  In fact, the 50% rule may not apply at all except as an average in large population studies, but may well be entirely irrelevant or even misleading to the understanding of X chromosome inheritance in genetic genealogy.

The X is still useful to genetic genealogists, just not in the same way that other autosomal data is utilized.  The X is more of an auxiliary chromosome that can provide information in addition to your other matches because of its unique inheritance pattern.

Unfortunately, this discovery leaves us with more questions than answers.  I found it incomprehensible that this phenomenon has never been studied in humans, or in animals, for that matter, at least not that I could find.  What few references I did find indicated that the X seems to recombine with the same frequency as the other autosomes, which we are finding to be untrue.

What is needed is a comprehensive study of hundreds of X transmission events at least 3 generations deep.

As it turns out, we’re not the only ones confused by the behavior of the X chromosome.  Just yesterday, the New York Times had an article about Seeing the X Chromosome in a New Light.  It seems that either one copy of the X, or the other, is disabled cell by cell in the human body.  If you are interested in this aspect of science, it’s a very interesting read.  Indeed, our DNA continues to both amaze and amuse us.

A special thank you to Jim Owston, Matt Dexter, Blaine Bettinger and Robert Paine for sharing their information.

Additional sources:

Polymorphic Variation in Human Meiotic
Recombination (2007)
Vivian G. Cheung
University of Pennsylvania

A Fine-Scale Map of Recombination Rates and Hotspots Across the Human Genome, Science October 2005, Myers et al
Supplemental Material



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224 thoughts on “That Unruly X….Chromosome That Is

  1. Hello Roberta, I have a a X chromosome situation going on here :-). My mother, her brother, me and my son all have share a considerable amount of X DNA with another family but no autosomal DNA. My daughter does not share any X DNA with the other family, Have you come across anyone sharing so much XDNA (50.4 cM) and no autosomal DNA.

    This is my mother’s shared XDNA with someone from the other family
    Chr Start Location End Location Centimorgans (cM) SNPs
    X 1982358 30249248 50.4 3921

    This my mother’s brother with the same person of the other family
    Chr Start Location End Location Centimorgans (cM) SNPs
    X 1982358 30232847 50.4 3242
    Largest segment = 50.4 cM
    Total of segments > 7 cM = 50.4 cM Actual.

    This is me with the same person of the family
    Chr Start Location End Location Centimorgans (cM) SNPs
    X 22803814 30230136 9.3 922
    Largest segment = 9.3 cM
    Total of segments > 7 cM = 9.3 cM Actual.

    This is my son with the same person of the other family
    Chr Start Location End Location Centimorgans (cM) SNPs
    X 22906823 30230136 8.7 897
    Largest segment = 8.7 cM
    Total of segments > 7 cM = 8.7 cM Actual.

    • The X is sometimes passed intact from one ancestor. In other words, your daughter may have received one of your X chromosomes from one ancestor and none from the other. To sort through this would take some map-drawing and maybe some additional relatives.

  2. I found out through that I have 3 % British ancestry in me but my family comes from eastern Europe (Germany, Poland, Austria, Slovakia) How would I know where this gene came from and from what generation? Where would I look to find out the family that contributed that gene.

  3. I am wondering what impact on my X Chromosome does it make where my mother’s father’s mother’s mother (g-g-grandmother) is the same person as my father’s mother’s mother’s mother (g-g-grandmother). The chart shows I would get 12.5% from each one due to their position but does it increase the % that I would get from her? Or increase the likelihood of getting more?

      • So let’s say that on FTDNA, Katie matches me at 29cm on my X chromosome (and she also matches me on other various chromosomes at a level making her around a 2nd cousin something or other). I downloaded the full chromosome browser spreadsheet, and found all of the people who overlap with Katie on the X. However, when I did a Matrix Match with them on Katie, then they don’t match autosomally. So although they overlap on the X with Katie, they don’t appear to be genetically related to Katie. Is that correct?

      • By the way, I have already matched and Matrix Matched the autosomal matches (we need less ambiguous terminology) with Katie, so I know who her true matches (lol – IBD) are. I’m trying to make sense out of the X-overlap people with Katie but who don’t match her autosomally.

        • Keep in mind that the matrix only looks at people who match above the threshold of total 20cM and a largest segment of 7cM. When you download your matching segments, you get much smaller ones than that too.

  4. Roberta, I enjoyed your article very much and learned a lot from it, but I want to make sure I am seeing typos and not assertions of fact in two places. In your first two column spreadsheet it looks like you missed the 3G-GP generation and that threw off your percentages. Please confirm. Secondly in both spreadsheets you use 12% as the contribution of GP’s, which I believe (from other numbers in the article) should actually be 12.5%. Please confirm. Otherwise, well done, thanks.

  5. Hi Roberta, on Gedmatch, I have a female match of X CM only of 30.6, no Autosomal match. In comparison, I share 35.7 X CM with my 1/2 sister. (of course I also share Autosomal). When I compared her Gedmatch list to mine, we have 22 common names. Can you tell me if I am related to this X match?

  6. I am hoping you can shed some light on a mystery. I have recently connected to a young man that could be as closely related as my first cousin. Neither he nor I know who our biological fathers are but do know our mothers. We have not found a link between the families yet but clearly there is one between the two of us. Can you give me your impression of what the results could mean? After doing an x-dna comparison this is the result:

    Chr St loc. End loc. cM. SNPs
    X. 488604. 133841337. 150.5. 13818

  7. Hi Roberta–
    Thanks for this posting. I am curious about your heading that the “X chromosome doesn’t recombine as expected”–isn’t this outcome a result of the fact that the X chromosome is only one chromosome, 180 centiMorgans long, while the autosomes are both more numerous and represent many times more opportunities for recombination? So, one could apply the same reasoning to any individual chromosome, it is just that the math of the autosomes works out so that the inheritance looks more evenly distributed. Wouldn’t you see a similar pattern if you were focused on a particularly large segment on a single autosome? I just wanted to clarify this for my own understanding.

    • Jonathan, you are correct that any chromosome can be inherited in an all-or-none fashion from a grandparent. Look at generation 2 in Figure 2 of Graham Coop’s blog:

      I have a case in my own family where the entire length of chromosome 4 has been inherited intact through at least five and maybe six transmission events.

      I suspect there’s a bit of ascertainment bias going on here: if you notice something that strikes you as “odd,” you are more likely to notice if it happens again, and other people will chime in if they’ve seen the same thing. AFAIK, no one has collected a *random* sample looking at the X chromosome to see if it behaves any differently than other chromosomes of a similar size.

      • By the way, the autosomal match is 23 cm, longest match 9 cm. I will let you all know if I ever get more information.

  8. Thanks for a facinating article Roberta!

    I happen to be so lucky that I was able to test both of my grandmothers (paternal and maternal) and thus with my parents tested I have been able to determine many very interesting things about my personal autosomal DNA and how much of it I did inherit from which grandparent.

    But my point is that as your article points out X chromosome does not seem to recombine “normally” – I myself have inherited my X chromosome completely from my maternal grandmother (I am a male, thus I have only one X chromosome) with nothing from my grandfather.

    So I have been able to determine I have inherited 21,6% from my paternal grandfather, 28,4% from my paternal grandmother, 20,5% from my maternal grandfather and 29,5,% from my maternal grandmother.

    • Vernon, it’s an interesting theory to think that inactivation and recombination are somehow connected, but a quick look at the data in this article shows it’s unlikely.

      There are two granddaughters in the table above. Both inherited a single chromosome from their mother, which is a combination of the mother’s chromosomes which she inherited from the maternal grandparents. Yet there is no preference for one or the other. One chromosome is highly-favored in one instance (granddaughter 1 inheriting 168cM from her MGF and only 29cM from her MGM) while the other chromosome is favored in the other (granddaughter 2 inheriting only 20 cM from her MGF and 176 cM from her MGM).

      Since, in females, the same x-chromosome is switched off in every cell of the body, there seems to be no correlation in this data set between the inactive X and whether it is favored or unfavored during crossing over.

      • Dave, it may be that X-inactivation has nothing with X-inheritance, but what you said in your comment is not true. The inactivation takes place in the embryo stage and at that stage some cells have one X inactivated while other cells have the other X inactivated and it is random. When the embryo develops these cells replicate so regions of the female have one X active and other regions have the other X active. This is the explanation for calico and tortoiseshell cats having 3 color coats, since in cats the coat color is X linked. The following quotation is from this article (
        “In some brains, for example, a mother’s X chromosome was seen dominating the left side, while the father’s dominated the right. Entire organs can be skewed toward one parent. Dr. Nathans and his colleagues found that in some mice, one eye was dominated by the father and the other by the mother. The diversity even extended to the entire mouse. In some animals, almost all the X chromosomes from one parent were shut; in others, the opposite was true.”

  9. X inactivation is a fascinating topic, but I don’t know of any research to show that it affects recombination. The inactivated chromosome uncoils during replication for cell division and recombination. Roberta posted another blog just yesterday, where she demonstrates that the all-or-nothing inheritance of a grandparental chromosome happens on the autosomes as well. As I mentioned above, I suspect there was a bit of ascertainment bias in reports of this happening on the X. People just noticed (and thus reported) it more.

    • To your point, Dr. Turner, the genome comparison between my father and daughter at 23andMe shows matching across all of chromosomes 9 and 21. It also shows that on chromosomes 7, 15, 17, 18, and 22, they have no matching at all.

      So altogether, it looks as if my daughter inherited seven autosomes from me with this “all or nothing” characteristic. The remaining autosomes varying from having “just a little sharing” to “quite a lot”, and it seems to balance out overall. The total sharing between my father and daughter is 47.5%.

      So, to get back to the X chromosome …

      I fully expected my three sisters to match on the entirety of their paternal X chromosome, and they did. But what I hadn’t really expected was that one of my sisters matches one of my brothers on the entirety of their maternal X chromosome.

      What’s more, I match both of these siblings on the X chromosome — with the exception of a 20 cM region surrounding the centromere.
      Thanks to several matches in this region, I’ve been able to identify its source as my maternal grandmother.

      The rest of the chromosome is from my maternal grandfather — which I’ve been able to confirm on the basis of dozens of matches. One match, in particular, is a good illustration.

      There is an individual who shares three segment with me on the X chromosome, versus only two segments with my siblings. However, while the first segment is the same for all three of us, my siblings’ second segment begins where my second segment does and ends where my third segment does. I’m “missing” 20 cM my siblings’ match on our grandfather’s side, thanks to the “intrusion” of DNA from our grandmother.

      I have three other siblings (the other two sisters and another brother). Two of them inherited more of the X chromosome from our grandmother than from our grandfather, while the third inherited all but 49.4 cM at the beginning of the chromosome from our grandfather.

      You might think that among the six of us, we’d have inherited all of both of our mother’s X chromosomes. Instead it looks as if there’s at least an 18 cM stretch at the end of the long arm of the chromosome where we only inherited DNA from our grandfather.

      I might also add that the brother whose X chromosome came only from our grandfather also has a daughter. That means it’s possible for her to trace the source of one of her X chromosomes to a single great, great grandparent: the paternal grandmother of her father’s maternal grandfather.

  10. Roberta, would a 3.41 cM X-chromosome match even be worth looking at? It’s the only X-match (other than me and one of our female first cousins) that my brother has on FTDNA, and the Total cM is 20.27 with this person.

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  12. Phased data from Gedmatch
    X chromosome
    1/2 brothers-same mother
    Comparing Kit PF404852M1 (Michael)(M) and PFN80425M1 (D R )(M)
    Minimum threshold size to be included in total = 700 SNPs
    Mismatch-bunching Limit = 350 SNPs
    Minimum segment cM to be included in total = 7.0 cM

    Chr Start Location End Location Centimorgans (cM) SNPs
    X 2,710,157 10,013,642 23.5 1,086
    X 128,787,527 149,034,194 37.2 2,701
    1/2 sibs, same mother
    Comparing Kit PF404852M1 (Michael )(M) and PF204898M1 (cynthia)(F)

    Minimum threshold size to be included in total = 700 SNPs
    Mismatch-bunching Limit = 350 SNPs
    Minimum segment cM to be included in total = 7.0 cM

    Chr Start Location End Location Centimorgans (cM) SNPs
    X 2,710,157 9,225,116 19.9 908
    X 148,374,123 154,551,755 14.2 943
    full sibs
    Comparing Kit PFN80425M1 (D R)(M) and PF204898M1 (cynthia)(F)
    Chr Start Location End Location Centimorgans (cM) SNPs
    X 2,710,157 9,225,116 19.9 957
    X 9,921,481 129,060,072 123.2 12,612

  13. X chromosome
    Comparing Kit PF404852M1 (Michael)(M) and PFN80425M1 (D R)(M)
    1/2 brothers-same mother
    Comparing Kit PF404852M1 (Michael Schlegel)(M) and PFN80425M1 (D R Smith)(M)
    Minimum threshold size to be included in total = 700 SNPs
    Mismatch-bunching Limit = 350 SNPs
    Minimum segment cM to be included in total = 7.0 cM
    Chr Start Location End Location Centimorgans (cM) SNPs
    X 2,710,157 10,013,642 23.5 1,086
    X 128,787,527 149,034,194 37.2 2,701
    1/2 sibs, same mother
    Comparing Kit PF404852M1 (Michael)(M) and PF204898M1 (cynthia)(F)

    Minimum threshold size to be included in total = 700 SNPs
    Mismatch-bunching Limit = 350 SNPs
    Minimum segment cM to be included in total = 7.0 cM
    Chr Start Location End Location Centimorgans (cM) SNPs
    X 2,710,157 9,225,116 19.9 908
    X 148,374,123 154,551,755 14.2 943
    full sibs
    Comparing Kit PFN80425M1 (D R )(M) and PF204898M1 (cynthia)(F)
    Chr Start Location End Location Centimorgans (cM) SNPs
    X 2,710,157 9,225,116 19.9 957
    X 9,921,481 129,060,072 123.2 12,612

    Comparing Kit F404852 (Michael)(M) and FN80425 (D R)(M) 1/2 sibs same mother

    Minimum threshold size to be included in total = 700 SNPs
    Mismatch-bunching Limit = 350 SNPs
    Minimum segment cM to be included in total = 7.0 cM
    Chr Start Location End Location Centimorgans (cM) SNPs
    X 2,710,157 10,013,642 23.5 1,092
    X 128,787,527 148,644,876 36.5 2,712
    Comparing Kit F404852 (Michael)(M) and F204898 (cynthia)(F) 1/2 sibs same mother

    Minimum threshold size to be included in total = 700 SNPs
    Mismatch-bunching Limit = 350 SNPs
    Minimum segment cM to be included in total = 7.0 cM
    Chr Start Location End Location Centimorgans (cM) SNPs
    X 2,710,157 9,225,116 19.9 913
    X 148,374,123 154,551,755 14.2 963
    Comparing Kit FN80425 (D R)(M) and F204898 (cynthia)(F) full sibs

    Minimum threshold size to be included in total = 700 SNPs
    Mismatch-bunching Limit = 350 SNPs
    Minimum segment cM to be included in total = 7.0 cM
    Chr Start Location End Location Centimorgans (cM) SNPs
    X 2,710,157 9,225,116 19.9 961
    X 9,921,481 129,060,072 123.2 12,663

  14. Read this blog item again after observing the data I show below which seems to fall perfectly into your discussion. As surrogate for my mother in matching, I’ve been using her only surviving sister – I call her “Aunt Sue” below. I am male, the others are female.

    1. My X chromosome matches Aunt Sue with 129cM total / 69cM longest segment.
    2. My sister Sally matches Aunt Sue with 156 total / 97 longest segment.
    3. My niece Martha – the daughter of another (deceased) sister – matches Aunt Sue (her great aunt) with 195 cM total / 165 longest segment.
    4. I match sister Sally for 137 total / 69 longest segment
    5. I match niece Martha 69 total / 59 longest segment.
    6. Sister Sally matches niece Martha 120 total / 96 longest segment

    My understanding is that the X Chromosome is 197 cMs. If so, since she matches her great aunt with 195 cM, my niece Martha must have inherited almost the exact X Chromosome of her great aunt Sue from Sue’s sister – Martha’s grandmother – who then must have had virtually the identical X Chromosome (of course Martha’s mother must also have had the near-identical X chr). But if I, a male, inherited only my mother’s X Chromosome, should I not match niece Martha for the entire X Chromosome rather than just 69 cM? Where have I gone wrong in my thinking? What else might I infer from these data and how might I use it to best advantage elsewhere?

    • Hi Wallace,
      I am going to make a stab at trying to answer your question. You don’t give a name for your mother. I will call her Jane. Jane and Sue are sisters. They received an X from their mother and one from their father. The X from their father was identical for both of them, as he only has one to give them. But the X that Sue and Jane received from their mother, your maternal grandmother, was most likely not identical. It could, and likely was, an unpredictable mixture of dna from recombination of the X from your maternal grandmother’s mother and father.

      If Martha matches her grandmother, then it appears that for two generations, there was very little recombination of the X in her line. It also seems to indicate that your mother and her sister, Sue, did not inherit identical X chromosomes from their mother. This is why you do not match with Martha more than you do.

      Interestingly, if recombination in the X fails to take place in a fair number of eggs as they are formed, it is possible that there would be instances where two brothers do not share any dna on their X chromosomes! One inherits the mother’s paternal X and the other inherits the mother’s maternal X. That seems like an amazing result and might raise a few eyebrows!

      • Thank you for the clear explanation, Marley! Yes, I failed to account for the recombination, thinking erroneously that the X was passed intact similar to Y-dna.

  15. OK…. i Have one for the books:
    One of My daughters did not get any X DNA From my mother only from my father”on my side of the genetic tree”
    From her Grandpa my Dad she got A {2040.8 Total cM} {176 largest cM}
    X {196 Total cM} {196 largest cM}
    From her Grandmother My Mother she got {1560.7 Total cM} {largest cM 138.4}
    X {0 Total cM} {0 largest cM}
    Me to my dad.. A{3587.1Total cM} {largest cM 281.5}
    X {196 Total cM} {196 largest cM}
    Me to my Mom A{3586.3Total cM} {largest cM 281.5}
    X {196.1 Total cM} {196.1 largest cM}

    • This is exactly what the article is talking about. You did not recombine your Xes and sent your father’s X unchanged to your daughter.

  16. Hello,my name is randy,i have a real head scratcher here.on gedmatch my kit A675212 matches a female A246857,we share on the autosomal 292.8 cM total 48.8 cM largest.but now the x is the problem total 195.9cm largest 195.9 now on my tree she is to be my mothers half siblings daughter.but we are thinking maybe something else going on.i haven’t been able to match and dna to my mothers so called moms side of tree.i have over 30,000 people.but nothing pointing to the called grandmother or on up her it possible that my mother was somehow an aunt to edna???there where a lot of lies told down the wife and I have uncovered a ton of it.and set it right.but my mom is the only mystery hoping some one here can tell me more about this match.on facebook a few people told me that this match was very very rare.for a male and female to have like this thanks also my tree on ancestry randy_m6219 user name and tree is mystery roots thanks again

  17. Seems to me that match is in the range of a 2nd cousin, not a half-first cousin – the latter would likely be closer to 600-700 cM. My example: a 1st cousin shares 1,700 cm with me, my 2nd cousin shares 287 with me. The unpredictable X chromosome shows that she is on your mother’s side but I’d guess that it doesn’t mean much more than that (again, my example: a niece shares 195cM X chr. with her maternal great-aunt but only 1/2 to 1/3 of that with any of her aunts or uncles.)

  18. I have a GEDmatch with another female of 47.2 cM on the X chromosome with no autosomal match at all. We seem to have no immediate correlation between four generations of ancestors – would this be an example of a guerilla X chromosome at work?
    Start location = 40,748,881, End location = 110,071,352, SNPs = 8,026

  19. Interesting article. I found it after noticing that I shared none of my x-chromosome with my brother. I have two other brothers, who have not been tested yet. I went to and did x-chromosome matching and found only two people who matched me: my daughter (of course), and one other person. This other person is someone who I have worked out shares a common ancestor with me – my 7th-great grandparents. She shares about 13 cM with me. It surprises me that nobody else on gedmatch is a match at all, even though there are hundreds with somatic matches. My brother has zero matches.

  20. Is it really possible that second cousins could only share 85cm on the x chromosome and no autosomal? Could it possibly mean that the grandfathers do not have the same father?(the mothers are first cousins and the grandfathers brothers)

  21. Pingback: Concepts – Match Groups and Triangulation | DNAeXplained – Genetic Genealogy

  22. Hi, I am new to DNA, and understand SORT of, and normally ignore it due to ignorance and confusion, but after doing my DNA and my paternal sister’s DNA to confirm that she was indeed related, I had more questions, so ordered another test for my bio maternal 1/2 brother, and my maternal second cousin. My 2nd cousins results just came back and all looks fine, BUT the X. Both my paternal aunt and my maternal cousin have extremely high X match to me (GEDmatch). One on one comparison says the 2 are not related, and I am so confused. According to paperwork, there is no shared ancestry between sides that I can find. Interestingly enough, my cousin matches a large amount of family, but I do not. I think my mom was adopted maybe?

      • I’m sorry, I am female. So would the X be carried down from way way back in the past if that is the case? Or am I opening another bag of worms? For females, how can it be helpful?

  23. I think I may have been given incorrect Information. A kit that I manage (female) had a match on Ancestry (another female) at 1,950 cms across 63 segments. Someone said if I uploaded to Gedmatch and ran the one to one, the X would be 196 for half-sisters and anything less would be aunt/niece. We know these are the only two possibilities between these two matches given the info from the new match. Is that incorrect though? My understanding from this article is that is not true. Thanks.

    • That is incorrect. I’m not sure why one would think this. Even full siblings could have received one maternal X chromosome (the mother’s mother’s) for one child and a second maternal X chromosome (mother’s father’s) for the second child.

      • Roberta,

        Not only are you entirely right in your reply to Kim, I have a situation in my own family in which what Kim was told would lead a person to think that a niece was actually a half sister.

        Two of my siblings — a brother named Bernie and a sister coincidentally named Kim — match across the entire X chromosome. Obviously, since it’s the only one my brother has, this is obviously the maternal X.

        Anyway, Bernie has a daughter named Stephanie. Stephanie hasn’t tested yet, but as Bernie’s daughter her paternal X chromosome must match her father’s only X. Therefore, it would also match Kim’s maternal X chromosome.

        Since Bernie and Kim are full siblings, Stephanie would also be expected to share somewhere around 25% of her DNA with Kim — same as with half sisters.

        You can see the problem. Anyone who believed in the “test” mentioned by the other Kim would unavoidably reach the mistaken conclusion that Kim and Stephanie are half sisters.

        • Just thought I’d update this reply, since my niece Stephanie has now tested.

          My sister Kim’s overall matching with our niece is 26.5%. But as expected, they match across the full length of the X chromosome. Obviously, this is Stephanie’s paternal X and Kim’s maternal X.

          I will also note that since Bernie and I also match across the entire X — with the exception of a 20 cM region surrounding the centromere — my daughter Kathryn and her 1st cousin Stephanie match across the entire X apart from that same 20 cM.

      • I am confused now. It is my understanding that this would be exactly the scenario for paternal half-sisters. They would share 100% of the X because their common father would only have one X to share with them. The mothers’ X and the ability to give one daughter the grandfather’s X and one daughter the grandmother’s X wouldn’t come into play. Please explain what I am missing here. Thank you.

        • That is the case for paternal half sisters. If they shared mothers, they could receive different Xs, or different portions of Xs from her.

          • Thank you, Roberta. I am glad that my understanding was correct after all. 🙂 Have a blessed day.

    • It would be true if the half-sisters shared a father. He only has the one X chromosome to give them, so they’d share all of it. If the half-sisters shared a mother, anything from 0 to 196 is possible

  24. My daughter’s are half siblings and they share 1710 centimorgans across 72 DNA segments. On gedmatch they share 165.7 cM’ s on the X.

  25. Would love anyone sharing any ideas… I’ve tried to absorb the material but not sure its all clicking:

    Background: I originally believed my Father to be an NPE due to various reasons – late in life pregnancy, lack of resemblence to father, extreme size differences, etc.

    Had my Father and his half-sister (significantly older, from a more normal age pregnancy) tested. They shared about 925 cMs of DNA and 0 X-DNA. This suggests to me 1st cousins and that my Father is probably the son of my Grandmother’s only sibling, a brother.

    Combing through many DNA matches, I apparently have gotten fairly close and got a 149 cM match which then prompted me to reach out to a candidate and give them a test which resulted in a 198 cM match with 47 cM of X-DNA match.

    These results suggest to me a 2nd cousin match (though the 149 could suggest a 2nd cousin once removed but they’re both on equivalent levels on the family tree).

    Either way, this cements a set of Great Grandparents.

    The 198cM/47cM match’s Mother’s Mother’s parents are those Great Grandparents, meaning he should have received all of this X-DNA from his Mother who received half of hers from her Mother but ultimately only half of her total, who received all of hers from those Great Grandparents but ultimately all of her GrandFather’s and half of her available Mothers.

    Now, I know my Father received all of his X-DNA from his Mother but I don’t know if his Mother is the daughter of a son of the Great Grandparents or the daughter of a daughter. Can the 47 cM tell me any info?

  26. I agree, there are some odd things about X matches that need to be explored!

    However, I think it may be time to throw in another monkey wrench. While females evidently can pass on an X chromosome intact, and males must do so, I believe this tendency, if it is indeed something out of the ordinary, must ALREADY be factored into the human genetic map distances (in centiMorgans). The map distance between any two markers is simply 100 times the number of recombinant progeny divided by the total number of progeny. (In constructing the genetic map, these distances are corrected or adjusted by only considering the marker pairs that are closest together, so that double crossovers don’t artificially reduce the apparent distance between markers that are far apart.) In other words, the genetic map for the human X chromosome is by definition a statistical summary of the occurrence of recombination in whatever population or populations provided the data from which it has been constructed. (The gender of the offspring should have nothing to do with it, because gender is determined at the time of fertilization, well after meiosis has been completed, by the male gamete.)

    None of this, to my mind, explains the extreme difference in the number of X matches observed for apparently random males versus females (on GEDmatch, for example, using the default criteria). A quick tabulation of half a dozen of each this morning showed that females (unphased kits) get about 115 X-matches for every 1 X-match that males get (using the GEDmatch metric labeled “rows” on the X match report). Until this discrepancy can be explained and modeled mathematically, I don’t see how we can properly interpret our X matches.

  27. I am trying to come up with a practical application of this information. If x does not necessarily recombine as one would expect, and males get their x from their mother, and I am trying to find the father of a female adoptee, wouldn’t comparing x matches help to identify the mother or maternal line of her father, if I was focusing on a male with an x-match I highly suspect is on the adoptee’s paternal line?

    I am in the process of a detailed x match study on gedmatch and am amazed at the number of overlapping matches taking note of the supposed generational identifiers and how they may impact the matches. It is quite amazing.

  28. Pingback: Using X and Mitochondrial DNA Charts by Charting Companion | DNAeXplained – Genetic Genealogy

  29. By luck with a little help from some 2cd and 3rd cousins I was able to fully phase my X-Chromosome (a male so only the one), my sister’s, my maternal Aunt’s and my mother’s although she is no longer alive; My sister received her X-Chromosome from our mother with no crossovers; it is identical with my mother’s X-Chromosome from her mother. I had one crossover at position 100M; My mother actually had 2 crossovers from her mother, and her sister, my aunt, had 3 crossovers. So this is an average of 1.5 crossovers per person, with a range of 0 to 3; given the known range of crossovers per chromosome which obviously relate to their total length, this small sample appears to fall within a range that I would have anticipated as average behavior

  30. I have 5 full siblings. All of us have tested at 23andMe. My brother Bernie and my sister Kim match from 1-155,092,794 — or for 181.84 cM (which seems to be the full length of the chromosome, at 23andMe). This appears to have all come from our mother’s father, which would also mean it came from *his* mother.

    This has been very helpful, since I’ve come to believe that the people who raised him as were not his biological parents — even though that’s what we were always told, and what his birth record claims. (I should note, however, that my grandfather’s birth wasn’t officially recorded until 1963, when he was 59 years old.) Anyone matching my brother on his X chromosome is likely to be related through our maternal grandfather’s mother. (Not counting more recent relatives, of course.)

    I match both Bernie and Kim from 1-41,061,864 (65.58 cM) and 71,279,956-155,092,794 (96.31 cM). This basically means I only inherited about 20 cM of my X chromosome from my grandmother.

    The sibling who inherited the least from our maternal grandfather is my sister CJ. CJ matches Bernie from 9,855,801-51,585,484 (62.93 cM) and 142,626,795-155,092,794 (21.99 cM). Of course, she matches Kim for *all* of the X chromosome, but only because both sisters inherited a copy of our father’s X.

    Even at that, CJ still inherited over half of her maternal X chromosome from our grandfather — 96.92 cM versus 84.92 cM.

    Oddly enough, even with six of us we still managed not to inherit all of our mother’s X chromosome pair. There’s about a roughly 18 cM stretch at the end of our mother’s maternal X chromosome that wasn’t passed on to any of us.

  31. Pingback: Introducing the Match-Maker-Breaker Tool for Parental Phasing | DNAeXplained – Genetic Genealogy

  32. I still don’t understand all of this. I am wondering if someone estimated to be a second cousin could actually be my brother’s first cousin. I believe that they share the same grandfather, but they have different grandmothers. In addition for my brother the lineage is grandfather to my father and then to him. The person I believe is a first cousin has a lineage from the same grandfather to his mother and then to him. Again, they do not share the same grandmother. 23 & me has my brother’s cousin and him sharing 4.23% of DNA and 11 overlapping segments. Other documentation indicates that they are first cousins. Is this possible?

  33. Roberta, I just now noticed that my new found cousin, the biological son of my uncle, shares 10.1 X Chromosome match with his aunt. So, if her brother can’t pass along any X to his son, then I guess this means that this X has filtered down from his mother’s side? If I’m looking at this correctly, then that means we have a distant common ancestor with his mother. Right?

  34. I have been fascinated and baffled by my X matches and this explanation has certainly helped. I recently found 45 matches on GEDMATCH with whom I share at least one segment of X of at least 20 cM and yet the most autosomal dna I share with any of them is less than 200 cM. In fact, most of them share less than 100 cM of dna with me – some as little as 20 cM so obviously the shared X must have come from a long way back. I’m now feeling more confident of this possibility.

  35. Is an X match between two females a reliable indicator of affinity somewhere along our lines when no matches can be found on any other chromosomes? Thank you for your time.

  36. I have two females matching at 1391cm, but nothing on the X. Is it possible for them to be maternal half siblings? I was told that it is impossible, they have to be 1st cousins.

  37. So glad to have found this article, Roberta, thank you. I’ve just located a 2nd cousin, based on “regular” autosomal sharing with a group of 4 known cousins, and using some chunky X-DNA matches. And everything was exactly as expected except for one of the 4 known cousins whose X-DNA simply wasn’t there, and I was beginning to get very worried and confused. I can see now that she has apparently just failed to inherit X-DNA from her maternal grandfather.

  38. One thing that must always be kept in mind when matches aren’t as expected, sometimes the reason is that something is off on 23andMe’s end.

    Why do I say this?

    Well, recently my first sister’s daughter got her results back from 23andMe, and she has an 11.06 cM region at the beginning the X chromosome at which she matches none of my family members except for her mother and my father.

    Now, it’s fine that my niece doesn’t match any of her three maternal uncles at this location. The three of us didn’t inherit an X chromosome from our father. But, my niece doesn’t match either of her maternal aunts.

    This is odd, because they both match our father’s X here — and remember, he only has the one — and they match our niece’s mother. So, why don’t they match our niece? Well, the answer is: they do. The chromosome painting simply isn’t reflecting that fact. Why, I don’t know.

    I’d thought at first it could be a length issue, but the segment is 11.09 cM and includes over 700 SNPs. So this isn’t like a segment at which I match one of my sisters, but my daughter does not. In that case, the problem is that the segment includes fewer than 700 SNPs, and it is shown for me because it’s a female-male match; it isn’t shown for my daughter because it’s female-female. The SNP requirement is higher.

    I suppose what it might be is a chip issue, since my niece’s results would be from version 5 (which I personally think is a lousy chip), and everyone else’s are from v4 or v2-v3.

    My point is, there can be reasons other than the DNA itself why results may seem to be just a little “off”. [Note: this doesn’t account for things like not sharing any DNA at all with someone.]

  39. Hi, Roberta,
    Thank you very much for this article, it has clarified my doubts about the inheritance of the X chromosome. I have 68 matches in the same segment of the X chromosome in Gedmatch, between 10 and 20 cM. With some of them I share autosomal dna too. I have been told that this amount is rare and even more rare, that the surnames are of different ethnicities: British, Germans, French, Spanish, Russians, Poles, Italians, Jews and a Portuguese.
    In FTDNA I have 20% matches on the X chromosome, also with varied surnames but I am struck by the fact that I have 25% matches in the same segment of chromosome 9, some of which are also matches on the X chromosome.
    They are 3rd to 5th cousins or remote cousins.
    I do not know how to interpret this data. What do you think?
    Thank you very much and greetings!

    • Every situation is different. Before looking at X seriously, I require twice the number of cMs, and then I look at my pileup chart for things like you are asking. Then, use triangulation.

      • Thank you very much for the response, Roberta.
        I understand that the cM that I share are not significant and therefore very difficult to trace a common ancestor. I thought that they could indicate IBD or IBP but with so many different nationalities (with family trees of the last 400 years living in the same place) I discarded it. Maybe it’s about IBC.
        I’m not sure of my origin, it’s what I’m trying to find out. The different calculators do not fit at all in my family tree. I thought the matches on the X chromosome would give me some clue, but I see no. I have to wait for closer matches to appear.

  40. According to my understanding of my chromosome painting in 23andMe, my X is likely an exact copy from an ancestor at least 6 generations ago, from 200 to 300 years ago. This seems very unlikely unless certain X’s can simply turn off recombination entirely, which seems to have happened in this case. The X chromosome in question is North African, and the rest of my genes are nearly all European, so this entirely North African chromosome sticks out like a sore thumb. Unfortunately, I only have my mother’s DNA to look at, no more generations than that. She, too, has almost no DNA from this ancestor except one entire X chromosome, seemingly verifying that the ancestor is rather distant since she appears to have so little DNA from that ancestor. It seems that the idea that the X will recombine something like 75% of the time when it can doesn’t apply to some X’s which simply don’t ever recombine. If you are interested in checking this out, I can send you some screen shots. — David

    • Obviously, what counts here is the number of generations, not the number of years — generations can actually be long or short. For example, my mother had my brother when she was 18 years old. My father’s mother had her youngest son when she was 44 years old (and that wasn’t setting any records).

      While I can’t give you an example of an X chromosome being passed on from someone 6 generations ago, I can give an example of one passed on over 4 generations.

      The 4 generations are from my great grandmother (my maternal grandfather’s mother), to her 2nd great granddaughter (my brother’s daughter).

      I know that my brother’s X chromosome contains DNA only from our maternal grandfather — none from our maternal grandmother. We also have a sister whose maternal X chromosome fully matches our brother’s single X chromosome, and I’ve been able to confirm that the two of them have matches that collectively span the chromosome; and that all of these matches are on our maternal grandfather’s side. In addition, I match both of these siblings on my only X chromosome, EXCEPT for a roughly 20 cM region surrounding the centromere. Outside of this region, I have the same matches on the X that my brother and sister do. Within this region, I have matches to several folks who are descended from one or another of my grandmother’s maternal half sisters.

      So this accounts for three generations to receive an X chromosome from the same woman — (1) my grandfather; (2) my mother; (3) my brother and sister, and me (except for that 20 cM from my grandmother). Where does the 4th generation come in?

      My brother has a daughter, and of course since my brother only has the one X chromosome, that’s what he passed on to his daughter. Like her father, she matches our aunt across the entire X. She also matches my daughter in exactly the same way that her father matches me — everywhere on the X except for that 20 cM region.

      It’s possible that there’s actually a 5th generation to receive this same X chromosome. My niece has 5 children, including at least one son. (I *think* she has a 2nd son, as well, but I’ve lost track for the moment.)

      Since none of them has been DNA tested yet — as far as I know — there’s currently no way to tell whether any of them received an exact copy of their mother’s paternal X chromosome. If any of them did, that would be the 5th generation. And if it was a son, then there would definitely also be a 6th generation *if* that son eventually has a daughter.

      So, again, I’d say that it’s not only possible, it’s bound to have happened for someone. Based of the ethnicities involved in the rest of the genome and on the X by itself, I’d say you make that case.

  41. I am male. My mother, three full sisters, and myself all had are DNA tested at FTDNA. I have one match, a woman named Julia whom I share 7.71 cM of autosomal DNA and 195.93 cM of X DNA. FTDNA shows that I share 183.07 cM of X DNA with my mother. FTDNA does not show Julia as a match to my mother or any of my sisters. How is it possible for me to share X DNA with Julia when my mother does not?

    • It’s not possible for you to share more X DNA with Julia than you do with your mother. I would suggest that you contact support.

      • I am not concerned about the total amount of cMs that FTDNA states that I share with my mother, as Gedmatch indicates that we share 196.1 cMs. I agree with Danielle’s reply. My autosomal match with Julia appears to be on my father’s side and the reason I do not see Julia in my mother’s DNA matches is because she and Julia do not share any autosomal DNA. I understand that to mean that my mother must have passed me 196.1 cMs in X DNA that did not recombine in recent generations, which is why I match distant cousin Julia at 195.93 cMs on the X chromosome.

    • I have had a similar issue previously. It is possible that the autosomal dna comes through your father and then the X chromosome will not show up as a match to your mother because FTDNA will not match her with anyone who does not have autosomal dna with her even if the length of the whole X chromosome.matches. If you, your family and this female match were to transfer to Gedmatch you could see the matches that were only X matches.

      • It is certainly possible for an X chromosome to remain unrecombined over multiple generations. I mentioned my niece, for example, whose paternal X chromosome is 100% from a single 2nd great grandmother. A copy of this chromosome, apparently with no crossovers, was passed on my niece’s great grandfather to her grandmother to her father to her.

        That means it’s *possible* that my niece could share her entire paternal X chromosome with a 3rd cousin descended from the same 2nd great grandmother — although it would require that the same lack of crossovers also occur on the other line.

        It would also require that virtually no autosomal DNA be passed on. But this, too, is possible. The Shared cM Project shows the range of sharing between 3rd cousins as 0-217 cM.

        The single 7.7 cM autosomal segment shared between Jerry and Julia is small enough that it might not be “real”; or that even if “real”, a couple of no calls or miscalls for his mother might mean the segment would not show up for her — even if it should.

        The explanation that the autosomal segment could be from Jerry’s father’s side — so it wouldn’t be expected to show up for his mother — is also a possibility.

        But even if that explains the lack of X chromosome sharing between Jerry and Julia, it still doesn’t explain why Jerry shares less X chromosome DNA with her son than Julia does. As Roberta points out, no one can actually share more X chromosome DNA with Jerry than his own mother does — since 100% of any man’s X chromosome is from that man’s mother.

        The likeliest explanation would be no calls/miscalls. (Or, if either of them tested at a company other than FTDNA, there might simply not be enough SNPs on one side or the other for complete matching.)

  42. Amen! A very recent autosomal match with a 193.5 cm X match of a personally unknown relative with only 23.21 centimorgans greater than 1 cm. match, ( longest 9.4 ) in the other chromosomes, putting this relative well into 5th cousin or greater territory. As a male, an exact copy of my maternal grandmother or maternal grandfather. As Matt Dexler’s experience shows the probability of a mother passing on to a daughter and grandkids unmixed is above 0. While the paternal grandmother is good for 100 percent passing unchanged to their son’s daughters. The most likely but not certain heritage paths are father daughter father daughter etc.

    • If that’s on a kit where you used a service like Mapmy23, or DNA.Land where they “impute” or fix things, they may have imputed the X and then someone uploaded the file to another site. I’m seeing invalid X matches due to this. Just FYI.

      • Yes, I think it’s likely that the match is due to a synthetic kit based on DNA.Land’s imputation. They do not include any X data at all. FTDNA is looking for contradictions to a match to determine segment boundaries. If there is no data, there are no contradictions. Matt could contact his match to see if that’s the case.

  43. I (Female) have a DNA Match with a man who I share 504.8 cM’s of DNA with. I’m also a DNA Match with his sister who I share 349.8 cM’s of DNA with her + we’re an X-Match, Total segments = 69.2 cM (36.405 Pct). What would you say is the most likely relationship between my matches and I?

    • The brother and sister’s X-Match is Total segments = 86.1 cM (45.349 Pct) if that helps at all. I don’t understand X-Matches but it looks pretty close.

  44. Hi, I don`t understand why I have only 180 cM whith my daughter in genesis gedmatch. Why I don´t have 196cM?
    This is the chart:
    Chr B37 Start Pos’n B37 End Pos’n Centimorgans (cM) SNPs
    X 2,710,840 52,019,512 82.5 2,225
    X 77,372,275 110,649,855 22.7 939
    X 111,178,742 154,758,477 75.0 1,898

  45. Genesis introduces “hard breaks” in areas of low SNP density. Put a check in the box to prevent hard breaks.

  46. Greetings, I see this is an older article but I have an interestingly anomalous X story. I think it may be a situation of either A: a cousin with a distant cousin X (NO ONE ELSE has a trace of X on that side and we link from a grandfather’s father, unless my tree is out of whack) The match is as high as 87cM according to 23andme data. It is a contiguous block as well. It is literally my Grandmother’s largest segment, and between my Grandmother, mother and myself it degrades only slightly, and the same is true for her daughter as well. Still working to triangulate using 23andme spread.

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