What does this X match mean?

[MisterAcoustic]

Hello,

I am adopted, and I have uploaded my kit to gedmatch.com. On there, I match a person on X. There is no autosomal match.

I am male, and they are male. The length of the longest match is 22 cM, and it is a full base pair match. Interestingly though, nearly half of the remaining parts of the chromosome also show a full base pair match - just none of the segments are long enough to register as a match. The image literally looks like a comb, with full base pair teeth.

This seems really curious to me - is it possible that this could be a closer match than the autosomal side would suggest? Does it mean something specific about how we could be related? I'm just wondering how such a match can arise.

Thanks in advance!

[hansonrf]

FTDNA reports male and female results as two characters per position. For a male, both characters are the same since there is only one chromosome. x matches between FTDNA kits are thus either full [both characters match] or none in GedMatch.

23andMe raw data has only one character reported for a male x.

[Germanica]

Matching only on the X chromosome doesn't mean anything as far as I know. Matching on an X chromo for males means the shared DNA must have come from your mother's side but the lack of shared DNA on any other chromo doesn't mean anything significant. It just means you happened to inherit shared DNA only on your X chromo, just like you could have another match who you happen to only share DNA on chromo 7 or 12 or any other one.

[Kathy Johnston]

Hello,

I am adopted, and I have uploaded my kit to gedmatch.com. On there, I match a person on X. There is no autosomal match.

I am male, and they are male. The length of the longest match is 22 cM, and it is a full base pair match. Interestingly though, nearly half of the remaining parts of the chromosome also show a full base pair match - just none of the segments are long enough to register as a match. The image literally looks like a comb, with full base pair teeth.

This seems really curious to me - is it possible that this could be a closer match than the autosomal side would suggest? Does it mean something specific about how we could be related? I'm just wondering how such a match can arise.

Thanks in advance!

I agree with the others who have commented. Two males with a 22 cM match is significant and most likely identical by descent but we still can't tell how far back in time the most recent ancestor is. That is because a cousinship calculation by using the X alone is practically impossible.

Look at Blaine's probability chart here: http://www.thegeneticgenealogist.com.../NewChart5.jpg and you will see that some ancestors have a much higher chance than others (in the same generation) of contributing an X segment. If there are no autosomal segments that meet the threshold, then you are unlikely to have a close relative because most third cousins and below will show up as autosomal matches. So therefore, you are likely dealing with a more distant cousin.

That being said, I would still get ahold of your matching partner's pedigree chart and fill in the X chromosome ancestors. You might learn something about nationality and geographical origins. If the person tested here at FTDNA, he may be available to answer your questions since most people who transfer to GEDmatch are approachable and may know their X ancestors. If he tested at 23andMe he will have an M___ ID number and you can ask him to check his ancestry composition on the X and see what the Speculative, Subregional resolution shows. Be sure to ask him to look at Chromosome view and toggle over the populations. If he tested at Ancestry.com then his ID starts with A___ and he may have an extensive pedigree listed there and you may find collateral lines down to present. Finding ancestors in common would be difficult in any case.

Since you describe a what I think looks like many tiny segments (is that correct?) that match at GEDmatch then I think that is a sign that you share the same ethnic (population) makeup with this individual through the X chromosome and you may share a lot of distant geographically based ancestry on that line. Others could confirm this to be true because it is only a hypothesis based on a few examples that I have observed.

[MisterAcoustic]

Thanks for all your responses.

@hansonrf: The other kit was tested through ancestry.com. I'm guessing that it's extremely likely that they report 2 characters per position as well, since I only see either full base pair matches, or none... does that seem right?

@Kathy Johnston: Regarding the small/tiny segments - yes, there are a great many small matching areas. This is what made me curious, since in addition to the 22 cM full match, around 50% of the entire remainder of the chromosome shows as matching. I had seen the probability chart before, but never paid close enough attention to the actual numbers - very interesting.

I will try to follow up with this person to see what I can learn, even though it might not be the best lead. I'm still hopeful that one oddball piece of information might provide the key to the whole puzzle.

Thanks again.

[Kathy Johnston]

Thanks for all your responses.

@hansonrf: The other kit was tested through ancestry.com. I'm guessing that it's extremely likely that they report 2 characters per position as well, since I only see either full base pair matches, or none... does that seem right?

@Kathy Johnston: Regarding the small/tiny segments - yes, there are a great many small matching areas. This is what made me curious, since in addition to the 22 cM full match, around 50% of the entire remainder of the chromosome shows as matching. I had seen the probability chart before, but never paid close enough attention to the actual numbers - very interesting.

I will try to follow up with this person to see what I can learn, even though it might not be the best lead. I'm still hopeful that one oddball piece of information might provide the key to the whole puzzle.

Thanks again.

Yes, when the Illumina chip reads each position on the chromosome it assumes two alleles even if there is only one. That is true for FTDNA and Ancestry.com. So the double match is really an illusion.

Triangulating on the X chromosome with other people may eventually help you find a common ancestor. You may already be aware that if you find several others who match on the same segment, you increase the likelihood of finding an ancestor. Even small segments can be significant for a male on the X because there is not the same likelihood of pseudo-segments caused by having two Xs. That just means the sensitivity of the test is higher for a male.

Here is one site that you may be interested in if you have FTDNA data. http://www.dnagedcom.com/adsa/adsav1/index.php
Not too many people have successfully found an ancestor through an X match alone but that will increase as we reach a critical mass of people ordering the tests. FTDNA customers need to be aware that they may not have all their X chromosome matches listed since you need to match first on the autosomes to show an X match in the FTDNA browser. It helps to have other third party options like GEDmatch and the ADSA.

[prairielad]

.............

Since you describe a what I think looks like many tiny segments (is that correct?) that match at GEDmatch then I think that is a sign that you share the same ethnic (population) makeup with this individual through the X chromosome and you may share a lot of distant geographically based ancestry on that line. Others could confirm this to be true because it is only a hypothesis based on a few examples that I have observed.

While this may be possible (indicating shared geography), depending on size of segments, I think it is more due to fact that at any given position everyone has a 25% chance of matching as there are only 4 possible values for each position.

For example attached picture is my father to me(Male) on X.
His X is from his Romanian born mother, my X is a combination of my mothers paternal Grandmothers Swedish X and her maternal/paternal Grandparents English X.
Level set to show 100 SNP and 1cM length.

[hansonrf]

Thanks for all your responses.

@hansonrf: The other kit was tested through ancestry.com. I'm guessing that it's extremely likely that they report 2 characters per position as well, since I only see either full base pair matches, or none... does that seem right?

Thanks again.

Yes. I think Kathy's response gives us the explanation why.

[rasha]

if he tested at 23andMe he will have an M___ ID number and you can ask him to check his ancestry composition on the X and see what the Speculative, Subregional resolution shows. Be sure to ask him to look at Chromosome view and toggle over the populations. If he tested at Ancestry.com then his ID starts with A___ and he may have an extensive pedigree listed there and you may find collateral lines down to present.


__________________
NOOR

[richard86]

Hello, I've got a similar query regarding X DNA. I've just got Family Finder results for my dad which I uploaded and checked on Gedmatch and noticed that he has a number of matches on the X chromosome who share absolutely no autosomal DNA. For instance his top X match has 21.1 cM.

Also, I don't know if it is significant, but the matching segment on the chromosome browser shows up almost entirely in green ("base pairs with full match"). I only say that because when I look at other examples there is a lot more yellow "half match" - I need to educate myself, I know!

Is it worth contacting people who seem to match quite strongly on the X but share no autosomal DNA?

Many thanks,
Richard

[loisrp]

With your dad's X-match, you can consider it the same as if his mother had that X-match, because of how the X is inherited. Does your dad have endogamous ancestry? That might be what the green is indicating. If he is matching with a woman, the X-match might be switching between paternal and maternal sides of her chromosome. But most likely, this is a valid match, even if a small bit of it isn't.

You can run People Who Match Both Kits to get an idea of what side the match is coming from. Knowing this match is for your dad's mother, the X that your dad's mother had must come from her mother or her paternal grandmother. So now you are looking for this match to be on your father's maternal grandmother's line, or your father's maternal grandfather's mother's line (look at an X inheritance chart to see what I'm saying).

The fact there's no autosomal match suggests this is probably 4th cousin or equivalent at least, and maybe further.

[richard86]

Hi, thanks for your reply. I don't think there is endogamous ancestry, the match is with a male so I wondered if that could be why there is so much 'green'!? It is kind of a moot point anyway as given the likelihood that this is probably a quite distant cousin I'll probably not do much more with it at this time as my tree doesn't go far enough back on the lines of X inheritance to have much hope of finding a connection. It was interesting to hear your thoughts.

Cheers,
Richard.

[loisrp]

It's still worth asking in case the match has a family tree himself. It might guide you in a certain direction. With the match being a male, you know it's his mother's side you should look at. So already you've narrowed down things a lot.

When matching with a male to male, each has only one "side" to the chromosome. I'm not sure if that will result in everything looking green, compared to a comparison to a woman.

[snetphilie]

One thing nobody ever seems to mention is the fact that part of the X chromosome recombines with the Y Chromosome.

So it is in fact possible for you to inherit part of your X chromosome from your mother's father's father. Your mother's father's X partially recombined with his Y, so one of your mother's X's contains a portion of her father's Y, and then her two X's recombine and you likely get some of that passed onto you.

The same holds true for your father. Part of his X and Y recombined, so if you are male, you received part of the X he got from his mother in your Y chromosome, and of course the rest of the Y from him, but even his Y was a combination of his father's X and Y. If you are female, you still receive part of the Y that your father got from his father.

Moral of the story is, the X match doesn't filter out the part of the X that recombines with the Y, so it is not a very accurate indicator of anything.

Oh, and here's a video that shows how the X/Y recombination is different than the other chromosomes! https://www.biointeractive.org/class...n-y-chromosome