WikiTree Uncovers X-Chromosome Ancestral Treasure!
by Peter J. Roberts

WikiTreers who have tested their autosomal DNA (auDNA) with 23andMe, AncestryDNA, or Family Tree DNA’s Family Finder have an often overlooked treasure “buried” in their test information. These DNA results harbor some of their ancestors’ X-chromosome (X-DNA). The inheritance of X-DNA  is relatively complex (see video) and so WikiTree provides a simple tool to uncover which ancestors could have contributed to their X-DNA.

Begin your treasure hunt by registering at www.gedmatch.com and following their instructions to upload your DNA results. This will allow you to uncover X DNA segments you share with your cousins who tested with 23andMe, AncestryDNA, or Family Finder. Then enter your GEDmatch ID to your DNA Tests page in WikiTree in order for you and others to know who has X-DNA (and auDNA) results from those three labs.

If your ancestry is in WikiTree, then click on the link for “X-chromosome” on your DNA Ancestors View page under your DNA tab. This automatically creates a live tree of your ancestors who could have contributed to your X-DNA.  You should then e-mail that link to all your X-DNA matches and ask them, “Please let me know if you have any of these ancestors (or surnames) are in your ancestry.” Your cousins may have information you are missing about your shared ancestors. This also creates an opportune time to invite them to join WikiTree.

Some DNA results can be combined to prune your X-DNA ancestral tree. If you share an X-DNA segment with someone, but your mtDNA does not match their’s, then you can eliminate the ancestors on each your direct maternal lines as the contributor of that particular X-DNA segment. (More)

More adventurous treasure hunters can enter all the known descendants of a particular ancestor. Then click on that ancestor’s X-Chromosome DNA Descendants  to see which persons could have inherited that ancestor’s X-DNA. Test results of those living descendants could be used to “reconstruct” that ancestor’s X-DNA!

Having collaborative  crew members make for more successful treasure hunts, and the question on every seeker’s mind, “Why wouldn’t Mr. Crab share his treasure? A: Because he was a little shellfish.

Peter is an associate professor and archivist at Georgia State University. He has an undergraduate degree in art history from Emory University and a graduate degree in museum education from The George Washington University. He has had an interest in genealogy for about 40 years and has been exploring genetic genealogy for the past 10 years. He is the administrator for the Bahamas DNA Project and three surname DNA projects, namely Roberts, Sasser, and Rustin. He is a past regional coordinator for the Atlanta area for the International Society of Genetic Genealogy.

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  6 Responses to “WikiTree Uncovers X-Chromosome Ancestral Treasure!”

  1. How are you deciding just who is and is not an “X match”?
    Hopefully you are not using simple segment matching as you would for an autosomal DNA match (that would be atDNA, not auDNA).
    First, you must have a significant autosomal match to even look at the X. At GedMatch this is a minimum largest segment of 7cM and 700SNP’s; this is playing it safe, I prefer a minimum largest segment of 10cM (and I think GedMatch is heading that way).
    Then, from the GedMatch X FAQ, which I have copied and pasted below, the “X Match” must be greater than or equal to 3.5% of the total autosomal match and also exceed 1cM. This also is “playing it safe”. X matches do not define a “match”; they give you some hint as to where an autosomal match originates.
    Gedmatch X FAQ:
    X-DNA Comparisons-from Gedmatch FAQ

    Q. I have a close match on the X-DNA chart, but my testing company doesn’t show us as matches. Why?

    A. First, you have to understand that the inheritance patterns for X-DNA are very different than Autosomal matches. X-DNA is not passed from father to son. So, when you compare with somebody else where there is a father-son generation between you, your score will be zero. Otherwise, the genetic contribution is halved for each generation EXCEPT for mother to son, where it stays the same. Compare that to Autosomal DNA where the contribution by each parent is pretty much half for each generation – comparatively simple to understand.

    If a son was comparing his X-DNA to his mother, he would get a perfect score, about 196 cM. After that, the shared contribution goes down as you go further back in time – within the constraints described above. If a son was comparing his X-DNA to his father, he would get a zero score. A daughter would get a perfect score with either parent, since she gets a copy of X from each of them.

    Be careful when comparing 2 scores. The scores might be the same for 2 cases, but have very different implications. An ancestry which is through the straight maternal line for 3 generations might have about the same score as an ancestry which alternates male / female for 6 generations (see rules of inheritance in the first paragraph of this answer).

    Q. What is a significant result for X-DNA comparisons?

    A. X-DNA should not be used to determine the degree of a match, for the reasons stated in the previous Q/A. Having said that, a good rule of thumb for determining how significant the X-value is might be: “Any X-DNA comparison which results in a total cM value of at least 1 cM and also at least 3.5% of the total cM value produced by the autosomal comparison.”

    Q. What’s the best way to use X-DNA results?

    A. Use autosomal results to determine how closely related you are, and then use X-DNA results to help you narrow down the ancestral path. For instance, autosomal may indicate that you are 3rd cousins. X-DNA could help you determine if it’s straight maternal, alternating male/female, or something in between.”

    Posted with permission from and thanks to Curtis Rogers, GedMatch.

    The blog post referenced is excellent, BTW, but meaningless without an understanding of what an “X match” and how it relates to the required co existing atDNA match.

  2. Hello Laura, Thanks for your posting. See http://www.isogg.org/wiki/Autosomal_DNA regarding auDNA and atDNA. I prefer atDNA but a lot of people use auDNA.

    I’m not deciding what an X chromosome match is. Family Finder, 23andMe and GEDmatch are deciding. I recommend using their defaults. I believe it is about 7cM. If two males are a X chromosome match with each other then I expect the segment size can be a lot less than a 7cM. WIth a male to male match – a small shared segment is real but the shared ancestor likely lived long ago (earlier than known persons on one’s X-DNA ancestral tree).

    It is my understanding that Family Finder will not show any X-DNA matching unless you first meet their threshold for relatedness with that person on your autosomal DNA. Does AncestryDNA show X chromosome matching? If not, then that is another reason to upload to http://www.gedmatch.com and http://www.dnagedcom.com.

  3. So I have a match where I have two sisters who both match me on the X chromosome (female).
    Sister #1 has two matches with me 5.9 (50.4-67.9) and 11.1 (68.9-88.7) – so really pretty close to a very large match.
    Sister #2 has two matches with me 14.3 (50.6-87.5) and 2.6 (100.4-107.3). The 2.6 could be IBS.

    My Mum matches me for the full segment 195.9 (1.3-154.5) which is normal as there are two sides. Mum has a couple of small X matches with the two sisters that I am thinking must be IBS even though there is small small overlap?
    Sister #1 – 3.4 (53.8-67.9)
    Sister #2 – 3.2 (68.4-78.4) and 4.7 (130.6-135.5)
    Or could perhaps 53.8-78.4 be a maternal X match? but given sister 2 should share 53.8-67.9 with my mother and doesn’t, it lends to the theory that its paternal? Am I looking at this right?

    The funny thing is on the autosomal side, we only have lots of small autosomal matches.
    Sister #1 – Mum and I have have different small autosomal matches, largest 4cm. The only identical segment is on C03 – 3.3cm 63.4 -65.3.
    Sister #2 – Again we have different small autosomal matches, I have several > 4cm. The only identical segment is on C09. Mum has a 6.9cm (129.3-132.8) and I also share 4.4cm (130-131.9).

    Interestingly sister #2 tested at 23andMe, and no autosomal results were reported. Unfortunately only I tested at 23and me, not Mum so I can’t see her result there.

    Could I have an X connection on the paternal side and some distant maternal connection as well? Or should the whole maternal thing be discounted given such small segments? Where does the 3.5% come into this? From reading Curtis’ notes it sounds like I should abandon both of these as potential matches? If so, why would 23andMe reports just an X match if there was no automosal match to start with?

  4. Hello Veronica,

    Those two sisters are real cousins of yours to some degree. Do you have a sister? If so, like you, one of her X chromosomes is an exact copy of your father’s X chromosome which is mix of his mother’s two X chromosomes.

    GEDmatch can look at your autosomal DNA and determine if your parents are related to each other. Are they? You should ask your X-DNA matching sisters to also check to see if their parents are related.

    This is my first attempt at pondering a situation like yours. I suspect you and your mother are related to the two sisters through their mother. Part of me thinks the reason you match the sisters more than your mother does is because you are matching them via your father (i.e. your paternal grandmother).

    I hope you will encourage each of your X-DNA matches to add their ancestry and their GEDmatch ID to WikiTree.

    • Well… I wish I could edit that post, because if your parents are not related then I’m not sure how you match the sisters more than your mother does. If your match with them is via your father then why does your mother match them?

  5. Hi
    I have a match from FTDNA with a total of 39 cM. But on the X-Chromosome we share 195 cM. It is more or less the hole X-Chromosome. How could this be possible.
    We have just 6 common relatives of my total 2600 Matches. Could you estimate how close relatives we are. The other person is a lady.

    Best Regards
    Anders

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