When you test your autosomal DNA, your X-DNA is also examined and included in your raw data &/or match results. When you match someone on your autosomal DNA and also share segments on the X-chromosome, the unique inheritance pattern of X-chromosomes can help isolate your common ancestor to particular lines of your ancestry.
X-Matches in autosomal results
Family Tree DNA‘s Family Finder test identifies X-Matches with people you already match via your autosomal DNA, and displays them in your match list (see below).
You can also view the X-match detail in the FTDNA chromosome browser, and download all chromosome browser data to Excel or other software or sites for further analysis if desired (eg. GEDmatch).
23andMe X-DNA can be viewed in the 23andMe chromosome browser or downloaded, but only for those matches who choose to share genomes with you. The raw data can be transferred to GEDmatch for comparison with other kits in the GEDmatch database.
AncestryDNA does not provide or show any X-DNA information, so X-chromosome information can only be accessed by transferring a copy of the raw data to FTDNA or GEDmatch for analysis.
MyHeritage DNA does not yet show X-matches, but they announced at their Nov 2018 Live Conference that X-matches would be coming in future. You can upload a copy of your MyHeritage DNA raw data to FTDNA or GEDmatch for X analysis.
Living DNA does not yet report on X-matches, but will likely do so in the future when all their matching and features have been fully implemented.
X-Chromosomes
Your sex is determined by the X and Y sex chromosomes: chromosome pair number 23.
Males inherit a Y chromosome from their fathers and an X chromosome from their mothers. So all their X-DNA is inherited from their mother.
Females inherit an X chromosome from their fathers, and an X chromosome from their mothers.
A mother contributes an X chromosome that is usually a recombined mix of both of her X chromosomes (but not always), and fathers contribute their whole X chromosome intact to their daughters.
Because males only inherit an X chromosome from their mothers, if a male has an X-match in his DNA results, the shared ancestor must be on an ancestral line that follows the male X-inheritance pattern, as below (in green):
Because females inherit X chromosomes from both parents, if a female has an X-match in her DNA results, the shared ancestor must be on an ancestral line that follows the female X-inheritance pattern, as below (in green):
X-DNA cannot be passed down through two successive male generations.
Because some X-chromosomes pass down intact (through males) and skip a generation without recombining, and others are recombined (through females), the average expected percentage of shared X-DNA at each generation varies depending on the branch of the pedigree chart.
Compare the percentages across the same generations below.
For example, at the great-great-great-grandparent level, notice how the expected percentage of inherited X-DNA is only 3.1% on the far right direct maternal line, versus 12.5% on the left-most paternal line (and some other lines) at the same generation level.
With no X-DNA inherited from some ancestors, varying amounts of X-DNA inherited from others, the randomness of DNA recombination at each generation, and occasional segments passed down intact over several generations, X-DNA can be quite unpredictable and it can be difficult to identify exactly where it came from.
It is common to share segments of X-DNA with people who share no significant amount of autosomal DNA.
Males generally get far fewer X-matches than females.
X-DNA’s best and most practical use is for isolating matches to particular family lines, even though the amount inherited cannot tell you from whom or how far back it came.
Nor can the absence of any X-DNA disprove your relationship (except for immediate family members – see below).
Focus on larger X-matches, such as 20cM or more, as smaller segments may not be reliable (or may just be too far back).
For X-matches on FTDNA’s Family Finder, use the chromosome browser to check the segment sizes, as FTDNA includes very small segments (down to 1cM) in their total cMs, and you want to exclude those tiny segments and only count segments of 7cM or more.
Excel Surname Template
Click the image to the right to download an Excel spreadsheet surname template to create and print your own X inheritance pattern pedigree charts – create one for each person that you test (separate sheets for male & female charts).
Practical uses of X-DNA
- If a male shares X-DNA with a match, then the ancestor in common will be on his mother’s ancestral lines, according to the X inheritance patterns in the ‘Male’ charts above (as males can only inherit X-DNA from their mothers).
- If siblings have tested their autosomal DNA, and a brother has X-matches in common with his sister(s), then the sisters will know that those particular shared segments of X-DNA must have come from their mother, as their brother could only have inherited them from their mother.
- If brothers share very little X-DNA with each other, one would have inherited most of his X-DNA from his mother’s father and the other would have inherited most of his X-DNA from his mother’s mother, or they inherited the exact opposite of a recombined X.
- If brothers share most of their X-DNA, they would have inherited it either from the same maternal grandparent, or the same or very similar recombined X from both maternal grandparents.
- If half sisters with the same mother share very little X-DNA with each other, one would have inherited most of her X-DNA from her mother’s father and the other would have inherited most of her X-DNA from her mother’s mother, or they each inherited the exact opposite of a recombined X.
- If half sisters with the same mother share most of their X-DNA, they would have inherited it either from the same maternal grandparent, or the same or very similar recombined X.
- A daughter will share a whole X chromosome with her father.
- Full sisters will always share a whole X-chromosome inherited from their father (and they may share some X-DNA from their mother as well).
- Half sisters will share a whole X chromosome if they have the same father.
- You can attribute X segments to particular grandparents by comparing your X-DNA with cousins and other close relatives from each side of your family.
- Don’t forget to ask your match to look at the charts above and work out which of their lines you could match them on, to narrow down the possible branches from both sides of the family!
Useful Links
- X-Chromosome Webinars: Part 1, Part 2, Part 3 – FTDNA
- X-Chromosome Resources – ISOGG Wiki
- Unlocking the Genealogical Secrets of the X Chromosome – Blaine Bettinger
- That Unruly X Chromosome – by Roberta Estes
- How the X-chromosome helps with maternal vs paternal – Kitty Cooper
- Phasing the X-chromosome – Jim Owston
- X-Chromosome – The X-tra Special Chromosome – Emily Aulicino
- What does shared X-DNA really mean? – Kitty Cooper
- X-chromosome inactivation – NY Times
- What other types of DNA tests are available?
- X Chromosome recombination’s impact on DNA genealogy – Jared Smith
Thank you, was awake all last night thinking about the complexity, my grade school ‘Gregor Mendel’, peas etc just did not cut it. Now with a granddaughter, and having done the x and mt dna testing earlier in the year. Back to School!
Thank you for such an easy to understand explanation! I really appreciate the editable surname templates and can’t wait to use my new-found knowledge.
okay still a little confused here I have a match ( on ancestry and FTDNA) FTDNA gives X -DNA info both sites have the match as 1st-2nd cousin chromosome X
(start)1,370,495
(end) 31,816,956
(cm)54.97
(snp) 4,098
since X come from his mother and X come from my mother out common ancestor would be ?
FTDNA say was have 522 shared cm longest block 58
ancestry says Shared DNA: 492 cM across 27 segments
it should be noted I did the test with ancestry kit and upload the reults to FTDNA
any help much appreciated
Hi Michael, You are correct that your shared ancestor will be on your maternal side and his maternal side, as males can only inherit X-DNA from their mother. Have a look at the possible relationships that are consistent with 492cM. Eg. There is an 89.5% chance that your match is a Half 1st cousin (Half 1C; ie. you share one grandparent), or a 1st cousin once removed (1C1R; ie. he is a child of one of your 1st cousins, or his mother is a 1st cousin of your mother). There are other possible relationships, but if you know his age you may be able to eliminate some or all of them. If your match has a family tree, follow yours and his maternal X-inheritance paths (green in the male charts above) to look for common ancestors. If either of your family trees is unknown, you will need to build out the other and explore all possible relationships. Shared matches are very powerful clues. For example, if you both have shared matches through both maternal grandmother and maternal grandfather, you may be 1C1R. If you only share matches through one maternal grandparent (eg. grandmother), then you may be Half 1C (different maternal grandfathers). If there is a big difference in your ages, eg. one of you quite old and one quite young, explore the great-great and half-great relationships in the link above. Other considerations that may impact the possible relationships include the presence of endogamy, double cousins and multiple shared ancestors. Good luck! 🙂
Hello! I have a match on 23 and me that shows as an unknown half sister. We match 1350cm. Our x is an 83%match. Would this more than likely make us paternal cousins or is it still possible if our x isn’t 100% to still be half sisters and share the same father?
Hi Erin, sisters who share the same father share an entire X-chromosome, so you can’t be paternal half-sisters (presuming 83% is the half-identical amount shared). Have you considered the possibility of a maternal half-sister? That said, 1350cM is very low for a half sibling. If known shared matches indicate your match is on your paternal side, then explore the other relationships shown for 1350cM in DNA Painter’s relationship calculator. It uses the Shared cM Project data to estimate a 74% probability that a 1350cM match is either a grandparent, uncle/aunt, half-sibling, niece/nephew or grandchild; and a 25% probability of a 1350cM match being from a selection of other relationships (shown in the grey box). Scroll down further on the page to view a family chart with the possible relationships highlighted and impossible relationships faded out. If you know anything about your match or are corresponding with her, try to rule out some of the possible relationships based on age, geographic location, shared matches, etc. This answer may change if you share fully identical regions of X, multiple shared ancestors, or if you double cousins or from an endogamous population. Good luck, Erin – Regards, Louise
On my father’s side, I have Garvey/Lyons paternal so no X. Maternal mother Devery and her father’s parents were Whalen (F) and Devery. Her mother’s parents were Crehan from unknown Kerry and unknown father. I get matches that almost seem like they would match Garvey and Lyons, but this should not be. I suspect Crehan is somehow related to Garvey so I am picking up matches from this relation. Quite plausible since she was said to come over as an orphan with relatives. However, Garveys seemed to come over later but it could have been other relatives, not Crehans. would love to find out Crehan more than anything. Does this sound likely?
Hi Mary, yes you could have DNA matches who share through both sides of your tree, either through more than one set of your ancestors, or they may share with each other through different ancestors. Whether your described scenario sounds likely depends on the size of the X-DNA matches and where they fit in your tree. Re your paternal Garvey/Lyons, I presume Garvey is your paternal grandfather’s surname and Lyons is your paternal grandmother? As a female, you inherit a whole X-chromosome from your father, that he inherited from his mother. So you can have X-matches through your paternal grandmother (Lyons), but not from your paternal grandfather Garvey. Also consider that you could share both atDNA and X-DNA with a match, including segments from different lines (eg. atDNA from Garvey, but X-DNA from Crehan or another line). Be very careful with small segments too, as they may come from an ancestor too far back. Focus on larger X segments, say 20cM or more. (I’m not suggesting you exclude X segments down to 7cM, but don’t waste too much time on them either). For the shared matches, you might like to examine their shared segments in a chromosome browser or add them to a DNA Painter chromosome map to see if and where they overlap. Regards, Louise
Super helpful – many thanks!
Thank you for the feedback, Rivka! Regards, Louise
My mother matches another with 339cM largest is 48cM’s, I match with nearly half that, the largest being 28.. What relation would this make us?
Thank you in advance
Hi Christine,
Because your mother has tested, ignore the amount of DNA you share with the match and just use your mother’s shared amount (because you receive a sub-set of the DNA your mother shares).
I recommend using the free Shared cM Project relationship calculator to see possible relationships for shared cM amounts. Go to https://dnapainter.com/tools/sharedcmv4/339 (you’ll see I’ve entered 339 in the filter box at the top; you can enter any cM amount here to view possible relationships). The chart below it updates to show relationship probabilities for 339cM (or other amount you enter).
It shows a 49% probability that a 339cM match could be a great great aunt/uncle, a half great aunt/uncle, a Half 1st cousin (1C), a 1st cousin once removed (1C1R), a half great niece/nephew, or a great great niece/nephew. There is a 46% probability of a 339cM match beiing a 2nd cousin (2C), half 1st cousin once removed (Half 1C1R) or 1st cousin once removed (1C1R), and a 5% probability of a 2nd cousin once removed (2C1R). Note that there are some other relationships listed that fall outside the bounds of recorded ranges.
Scroll down further on the page and you’ll see a family chart with the possible relationships highlighted, and impossible relationships faded out. Each relationship box shows the average cMs that relationship shares (with low & high ranges in brackets).
Click on any relationship box and a pop-up will appear showing a histogram of actual amounts for that relationship:
cMs are along the bottom axis; you’ll notice 339cM is a bit on the higher side for a 2nd cousin. Explore other relationships. Use the shared matches and their family trees to try to work out which line of your mother’s pedigree that the match is on (presuming her ancestry is known). If her ancestry is endogamous (eg. Ashkenazi Jewish, Maori, Sicilian, etc), she could share multiple ancestors with the match so the cMs could be overstated.
Good luck – I hope this has helped! Regards, Louise
This has been extremely helpful, thank you so much! May I ask something? My son has an X-Match on FTDNA at 49cMs (longest block 24cMs and estimated at 2nd-4th cousin) but that person doesn’t match me on FTDNA!! Surely they must?
Hi Julie, I’m pleased it has been useful. The first thing to do with any X-matches on FTDNA is to check the size of the matching X segments in the chromosome browser. That is because FTDNA includes tiny segments in their totals, as small as 1cM, 2cM etc, and X-matches are not real matches if they are that small. I guess that would be the case with your son, as males can only inherit X from their mother, so his 24cM match will likely be on another chromosome (not the X), and he has some small segments on chromosome 23 that have caused the X-match label to display on the match list. We all hope that FTDNA will eventually exclude small segments in their totals, but for now we need to check via the chromosome browser. You may find that the longest 24cM segment is the only segment above 7cM, and that is the total shared amount with the match. If you don’t share with that person, then the match is likely through your son’s father’s side (and you can ignore the false X-match label). I hope that helps? Regards, Louise
Is one LARGE shared segment on the X chromosome more meaningful than 2 or 3 SMALLER segments of X-DNA? I ask because I have a new match with whom I share a single 50cM segment of X-DNA, but I have another match with a total of 57cM on 2 segments of X-DNA. Also, what if the total amount of DNA we share other than the X isn’t very high? Thanks!
Hi Ellen, unfortunately there’s not a simple answer for that, as it can vary in different instances. Generally though, one larger segment would be inherited from one ancestor, whereas a large total in smaller segments could include segments from more than one different ancestor, possibly further back. Or if the segments are adjacent to each other, it could be one larger segment that appears to have breaks in it due to mis-reads in the SNPs. Nevertheless, 50cM and 57cM X-matches are both good sizes that are worth following up using the X inheritance patterns. You could have a 50cM X-match who doesn’t share much atDNA. As an example, I had a 48cM X-match with a smaller amount of atDNA that was a confirmed 2C1R (2nd cousin once removed). Once you get to 2C1R and 3C (3rd cousins), some cousins won’t share atDNA with you, but they could still share some X-DNA with you. Definitely investigate X-matches of this size. If you can’t find the connection, put them aside for the future when new shared matches might help further, but if you can, that’s great. Good luck! Cheers, Louise
I share 70 CM with a possible cousin 3-4 or 5th..but my sister doesnt share any CM with this person.. why is that?
Hi Jade, it is not clear if you meant 70cM of autosomal DNA or X-DNA, but in either case once you get to 2C1R (2nd cousins once removed) and more distant, it is quite normal to match some people that your siblings don’t. You inherit 50% of your DNA from each of your parents, and your sister inherited a different mix in her 50% from each of your parents (that’s why siblings look different, as they each inherit a different mix in their 50% from each parent, unless they are identical twins). So where you share 70cM with a particular match and your sister doesn’t (eg. say the connection is through your paternal grandmother), your sister would have inherited the other grandparent’s segment in that location on the chromosome, so she will match relatives to your paternal grandfather (in that segment location), whereas you won’t match those cousins (presuming any have tested). That demonstrates how useful it is to encourage siblings to test. Up to 2nd cousins you should all share the same DNA matches, but beyond that you will each have some matches that your sibling doesn’t, and vice versa.
The information in this post on autosomal DNA might help, including this image depicting just one chromosome that shows how 3 children inherit different segments from their grandparents:
I hope that helps? Cheers, Louise
Louise can I have permission to use your diagram of autosomal DNA inheritance between grandparents, parents and 3 children in my upcoming presentation at Rootstech.
Hi Barb, Thank you for asking! Yes, you can use my diagram in your Rootstech presentation, providing it is clearly attributed to me and has a link to the website page where it appears. Regards, Louise
Hi Louise, I’m helping my cousin. She has an autosomal match with another female A of 842cm with an x of 90.3 on gedmatch. They would be one generation apart. We believe the connection is through my cousins paternal line and A’s Maternal Line. Would half sister between A’s mother and my cousin be a possibility or is there a more likely connection. Regards Brona
Hi Brona, The relationship you describe (half niece) is certainly very feasible, for the both the amount of shared atDNA (842cM) and the inheritance path of the X-DNA. If your cousin and A’s mother were paternal half sisters, they would share a whole X-chromosome (196cM) from their father. A’s maternal X-chromosome could include 90.3cM from her mother’s paternal X-chromosome and approximately 105cM from her mother’s maternal X-chromosome (she also has an X-chromosome from her father). Although this is certainly very feasible, make sure you also use the Shared cM Tool for 842cM and consider shared matches to check (or rule out) other relationships that might be possible. Good luck! Regards, Louise