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View Full Version : MISSING X MATCH WITH 2C1R COUSIN - MATERNAL



Antoni De Lake
09-29-2021, 04:42 AM
Hello

I have a question that my cousin Pete and I have been trying to solve for a few months and we cannot make sense of the lack of an x match between us when he has an x match with my mother and younger brother and sister

Pete and I share a common 2nd great grandmother and grandfather

The gedmatch 3D chromosome browser is attached below

From top to bottom + gedmatch kits

1. My mother NH9640768
2. Myself SR9980959
3. Younger brother HG9361458
4. Younger sister DC8092218
5. Cousin Pete LC171380C1 (2nd cousin 1 time removed)

You can see from the table below that my immediate family all x match, my mother, brother and sister match Pete and I don't.

Additionally even at 3cM, 25snps, prevent hard breaks Pete and I have no x match

I have NO x matches from 2,178 matches on familytreedna (FTDNA)

Can anyone explain this ?

Ibericus
09-29-2021, 05:47 AM
Edit: I don't know

C J Wyatt III
09-29-2021, 05:59 AM
Do your comparison again using high resolution, and you will see plenty of green for matching. If you think about it, males only have one X-chromosome to match on. For a given SNP, the chances of two males matching by chance is 0.5. To match 25 consecutive SNP's in a row by chance would be 0.5 to the 25th power, or about a 0.00000003 chance. By taking a strict probability based approach to matching, I am finding that minimum cM levels are an unnecessary constraint, and your example certainly supports that.

Remember X_one-to-many does not let you go below 7.0 cM minimum segment, so that kills off just about everything. I am having trouble finding one from the one-to-many which gives a match on the X_one-to-one using 3.0 cM. Clearly you have a lot of matching SNPs, but you are not getting enough in a row to get above the 3.0 cM minimum segment. I wish that you could still go down to a 1.0 cM segment on GEDmatch like one used to.

Antoni De Lake
09-29-2021, 06:07 AM
Thanks Jack

How would I achieve a higher resolution ?

I have used the x chromo gedmatch tool a 3cM (lowest setting) and 25 snps + prevent hard breaks which would normally show fragments that are centuries old ?

I am a Plantagenet descendant and have found ancient fragments from lots of distant relatives using this method, how do I set gedmatch to greater detail ?

C J Wyatt III
09-29-2021, 06:16 AM
Thanks Jack

How would I achieve a higher resolution ?



check box above 'window width'

C J Wyatt III
09-29-2021, 06:23 AM
Thanks Jack

I have used the x chromo gedmatch tool a 3cM (lowest setting) and 25 snps + prevent hard breaks which would normally show fragments that are centuries old ?

I am a Plantagenet descendant and have found ancient fragments from lots of distant relatives using this method, how do I set gedmatch to greater detail ?

I don't know if GEDmatch allows lower parameters with the paid Tier 1 Tools. The trouble with any match big or small is how do you know for sure who the common ancestor is. With X-matching I would not try to deduce anything more than a few generations back.

Pylsteen
09-29-2021, 06:48 AM
Your mother has two X chromosomes, one from her father and one from her mother; she transmits one of both, or a combination of both to her children; it could be very well the case that your siblings and cousin share X chromosome with your grandmother's family while you got the one from your grandfather (or other way around).

Antoni De Lake
09-29-2021, 07:34 AM
The trouble with any match big or small is how do you know for sure who the common ancestor is. With X-matching I would not try to deduce anything more than a few generations back.

We know who the common ancestor is. My 2nd cousin and I share 2nd great grandparents ... provable with birth records and known family history

I expanded the C23 window and it's still stating no segment match but I'm new to this

C J Wyatt III
09-29-2021, 07:48 AM
We know who the common ancestor is. My 2nd cousin and I share 2nd great grandparents ... provable with birth records and known family history

I expanded the C23 window and it's still stating no segment match but I'm new to this

The higher resolution will not cause GEDmatch to recognize a match, but I just wanted you to see that bunches of SNPs were matching. I might be considered a bit out of the mainstream, but I am trying to show hat your lack of declared matches by GEDmatch is nothing to be concerned about. According to probability, you are OK.

Antoni De Lake
09-29-2021, 08:15 AM
The higher resolution will not cause GEDmatch to recognize a match, but I just wanted you to see that bunches of SNPs were matching. I might be considered a bit out of the mainstream, but I am trying to show hat your lack of declared matches by GEDmatch is nothing to be concerned about. According to probability, you are OK.

Hi Jack, not concerned as I know we are related. I am interested in why there's no x match for a relatively close relationship. I can't find much online regarding this issue so it might be a rare occurrence.

C J Wyatt III
09-29-2021, 02:45 PM
Hi Jack, not concerned as I know we are related. I am interested in why there's no x match for a relatively close relationship. I can't find much online regarding this issue so it might be a rare occurrence.

I appreciate you sharing your example. It's not like your X-DNA data is missing, but it is broken up enough maybe with "no-reads" that the cM constraint gets you. It might be interesting to get your cousin's raw X-data and put it in a spreadsheet with yours and just do a manual comparison. That would be a good educational exercise.

Pylsteen
09-29-2021, 04:31 PM
Coming back on the point I made, I see that you do share X chrom segments with your siblings in your attachment; so indeed it seems to relate to some data issues

geebee
09-30-2021, 06:15 PM
Hello

I have a question that my cousin Pete and I have been trying to solve for a few months and we cannot make sense of the lack of an x match between us when he has an x match with my mother and younger brother and sister

Pete and I share a common 2nd great grandmother and grandfather

The gedmatch 3D chromosome browser is attached below

From top to bottom + gedmatch kits

1. My mother NH9640768
2. Myself SR9980959
3. Younger brother HG9361458
4. Younger sister DC8092218
5. Cousin Pete LC171380C1 (2nd cousin 1 time removed)

You can see from the table below that my immediate family all x match, my mother, brother and sister match Pete and I don't.

Additionally even at 3cM, 25snps, prevent hard breaks Pete and I have no x match

I have NO x matches from 2,178 matches on familytreedna (FTDNA)

Can anyone explain this ?

As has been stated, a mother can pass on a copy of either her paternal or maternal X chromosome, or she can pass on a recombined X chromosome composed of DNA from both.

To use a specific example, my mother had six children. Four times she passed on a recombined X chromosome that was made up of DNA from both her father and her mother. No two of these are exactly the same recombination, but with me the DNA is mostly from her father. Only about 20 cM surrounding the centromere came from my grandmother.

My other two siblings inherited an unrecombined* paternal X chromosome from our mother. Her firstborn, my oldest brother; and her fourthborn, my oldest (but younger) sister, match across the entire length of this chromosome. It's clearly on our grandfather's side, because all of their matches are on that side. (And collectively span the chromosome.)

Now, if two siblings can each inherit an unrecombined* X chromosome from the same grandparent, it stands to reason that it would be equally possible for two siblings to each inherit an unrecombined* X chromosome from opposite grandparents. Presumably this wouldn't happen frequently, but it's pretty much inevitable that it would happen sometimes. So the siblings could be completely non-matching on their respective maternal X chromosomes.

Keep in mind that I'm talking about siblings here. With cousins, there would be an even greater chance of having no matching on the X chromosome. It does, however, seem a bit more puzzling to me that you have no shared segments on the X chromosome among all of your matches at FTDNA.

Of course, as a male you will only have X matches on your mother's side. Which side are most of your matches on?

geebee
09-30-2021, 06:59 PM
Hello

I have a question that my cousin Pete and I have been trying to solve for a few months and we cannot make sense of the lack of an x match between us when he has an x match with my mother and younger brother and sister

Pete and I share a common 2nd great grandmother and grandfather

The gedmatch 3D chromosome browser is attached below

From top to bottom + gedmatch kits

1. My mother NH9640768
2. Myself SR9980959
3. Younger brother HG9361458
4. Younger sister DC8092218
5. Cousin Pete LC171380C1 (2nd cousin 1 time removed)

You can see from the table below that my immediate family all x match, my mother, brother and sister match Pete and I don't.

Additionally even at 3cM, 25snps, prevent hard breaks Pete and I have no x match

I have NO x matches from 2,178 matches on familytreedna (FTDNA)

Can anyone explain this ?

Looking at the graphics more closely, you can see that you and your siblings each match your mother across the full X chromosome. That's to be expected. But any of these might contain DNA only from her father; only from her mother' or from both -- and "both" is generally what is seen.

But if you compare yourself to your siblings, and your siblings to each other, you see that none of you inherited an identical X chromosome. Your brother and sister share the most DNA and the X chromosome, at 154.8 cM. But that's out of 187.7 cM. So there are over 30 cM where they don't match at all.

Also, you reportedly share 141.6 cM with one sibling, and 131.2 cM with the other. Again, this is out of 187.7 cM of possible matching. However, this leaves a lot of places where your siblings could share a 16.2 cM segment with your cousin that you do not share. It only has to be somewhere within one of their regions of overlap -- not yours.

Naturally, though, anywhere that your brother and sister both match this cousin on their X chromosome (or maternal X, in your sister's case), your mother will also match. (Technically, your brother and sister would not have to both match the cousin in the same place, but the fact that it's exactly the same size segment is somewhat suggestive of that.)

Antoni De Lake
10-01-2021, 11:36 PM
Of course, as a male you will only have X matches on your mother's side. Which side are most of your matches on?

I have a majority maternal matches on FTDNA but no x match which is very strange. I contacted FTDNA and this was their response



Request Update Request ID: 1285484

Hello Anthony,

An X match is determined by sharing X DNA with a match. It is not impossible to have no X matches, but I will check with our data assurance team to see if there is anything wrong with your testing.

Best,

Audley
Information Specialist
FamilyTreeDNA

Anthony de - Sep 27 2021, 08:21 AM
Request Form:
Hello, how is it possible that I have no x matches from 2,178 family finder matches ?

No further response from FTDNA , I have also conducted mtfull and BigY tests with them

I ended up with a new yNDA terminal of R-YP3929 , it is now R-FT62520, there are 2 of us on this terminal

MAbrams
03-27-2022, 04:40 PM
2nd cousins share a predicted 3% of DNA. You are 2nd 1r, so 1.5% is predicted. For the X chromosome of (rounded off) 200 cM, that would be 3 cM. So you would be lucky to see an X match

The above math is for all-female lineages. The numbers for you would go up, depending on how many males are inserted into your X lineages. But regardless, the predicted X won't be high. Your results tend to confirm that, as your X matching examples were only 16 cM. Your sister and brother were lucky to get the match. You were not. There is a lot of luck in X matching.

The X matching from your mother to you vs your two siblings is not identical. So its easily possible for cousin Peter's modest 16 cM match to show up on a region of the X that your siblings inherited from your mother, that you did not. You probably have many autosomal segments from various matches that you inherited from your mother, that your sibs did not.

~~~~

As for your lack of X matching on FTDNA, this is probably not that unusual. Males do not get a lot of X matches. I have a ginormous total of 8. My mother has over 1000 (presumably most of these are shaky). Also, beware, that you might have X matches at FTDNA that are under 10 cM. These are not shown on the main Views, and are only visible via the Chromosome Browser. Sort your X matches from High to Low. Check to see if your top X No Matches might actually show X from 6 to 10 cM. You might have some X segments from 6 to 10, or you might not.

The other thing is that FTDNA only shows X matches if they also have an autosomal match, so that cuts your number of X matches severely, compared to sites like 23andMe and GEDmatch, which do show X-only matches.

geebee
03-31-2022, 01:56 PM
2nd cousins share a predicted 3% of DNA. You are 2nd 1r, so 1.5% is predicted. For the X chromosome of (rounded off) 200 cM, that would be 3 cM. So you would be lucky to see an X match

The above math is for all-female lineages. The numbers for you would go up, depending on how many males are inserted into your X lineages. But regardless, the predicted X won't be high. Your results tend to confirm that, as your X matching examples were only 16 cM. Your sister and brother were lucky to get the match. You were not. There is a lot of luck in X matching.

The X matching from your mother to you vs your two siblings is not identical. So its easily possible for cousin Peter's modest 16 cM match to show up on a region of the X that your siblings inherited from your mother, that you did not. You probably have many autosomal segments from various matches that you inherited from your mother, that your sibs did not.

~~~~

As for your lack of X matching on FTDNA, this is probably not that unusual. Males do not get a lot of X matches. I have a ginormous total of 8. My mother has over 1000 (presumably most of these are shaky). Also, beware, that you might have X matches at FTDNA that are under 10 cM. These are not shown on the main Views, and are only visible via the Chromosome Browser. Sort your X matches from High to Low. Check to see if your top X No Matches might actually show X from 6 to 10 cM. You might have some X segments from 6 to 10, or you might not.

The other thing is that FTDNA only shows X matches if they also have an autosomal match, so that cuts your number of X matches severely, compared to sites like 23andMe and GEDmatch, which do show X-only matches.

I have to disagree with some of what you've said here, especially this:

"The above math is for all-female lineages. The numbers for you would go up, depending on how many males are inserted into your X lineages. But regardless, the predicted X won't be high."

I agree with the basic premise, but I think you seriously underestimate just how much the numbers can go up, with the result that the predicted X matching actually can be high. This is because unlike with autosomal ancestors -- whose number has the potential to increase exponentially in each preceding generation -- the increase in X chromosome ancestors follows the Fabonacci sequence.

For males the potential contributors are 1 in the parental generation, 2 in the grandparental, 3 in great grandparental, 5 in 2nd great grandparental, and so on. But any time that one of these potential ancestors proves not to have contributed anything to the X chromosome, then everyone earlier in that line falls out.

My brother, for example, inherited an X chromosome that contains no DNA from our maternal grandmother. So he can ignore great grandparents and so on on this side as possible contributors. In fact, it's as if he received his X chromosome directly from our maternal grandfather's mother. The same thing is true for one of our sisters, who matches my brother's entire X chromosome. This what somewhat of a surprise, since I only expected her to have that kind of matching with our other sisters, since they have an identical paternal X chromosome.

I match both of these siblings on all of the X chromosome except for about 20 cM surrounding the centromere. This is the only part I inherited from my mother's mother -- all the rest of my single X is from my mother's father.

Now, I still don't have what I would consider a "ginormous" number of X matches at FTDNA, just 21 in addition to my five siblings and my daughter. But as you've pointed out, FTDNA only includes X chromosome matches when there is also at least one shared autosomal segment.

At GEDmatch, I actually have several hundred X chromosome matches, including many dozens that are greater than 20 cM in length.

The largest of these is to someone who is my 3rd cousin twice removed. Actually, this is just the closest relationship. We're also 4th cousins once removed, and 4th cousins twice removed by three different paths. But of the various ways we're related, it's only by one path that we share our X chromosome DNA.

This path leads to my 4th great grandmother, Rachel Jones. To my cousin, she's both a 2nd great grandmother and a 3rd great grandmother, but it's only by the latter path that she could have passed on any X chromosome DNA to my cousin. But we share two segments on the X chromosome, one of
25.8 cM and one of 40.4 cM.

For our degree of cousinship, these are not trivial in size. But the path on my cousin's side alternates female and male, starting with Rachel Jones. On my side, the path is also alternating female and male, with a single exception. Obviously, in the male-female transmissions, no further recombination could occur.

I might also note that no only do my siblings and I -- including my brothers as well as my sisters -- have lots of X chromosome matches, but these (collectively) span nearly the entirety of the X chromosome. In part this may simply reflect just how many descendants the relevant contributors left behind -- and, of course, how many have chosen to do DNA testing.

But the bottom line is, there's no real reason to suppose that males should have very few X-chromosome matches. In fact, as a general rule they ought to have about half the number their mothers do, once you correct for false matches. The greatest number of these will occur in female-female comparisons, and the least number will be in male-male comparisons.

sirdan
04-19-2022, 12:22 AM
The key is the third table.

Pete match only on first small part of chromosome X (position range 27.... to 98.... You match with siblings out of this range of chr X. Long story short, you have inherited different segments and Pete.

How is that possible.

You and Your siblings match with mother of course, at that beginig (from 27...) but mother have two X chromosomes (one single from father and one from mother -crossovered). And boys have only one X, so they have different segments because XX crossovered differently from mother.

You match at beginning chromosome X with mother but on maternal side of mother, while others match with mother but on paternal side of mother (mentioned grandfather?).

You have no X matches on FTDNA, because I guesss you have no people tested of maternal line of your mother, and you matches mainly from that maternal side of your mother, am I right?

Anyway, look at this table https://familysearch.brightspotcdn.com/dims4/default/3910696/2147483647/strip/true/crop/1670x1221+0+0/resize/800x585!/format/jpg/quality/90/?url=https%3A%2F%2Ffamilysearch-brightspot.s3.amazonaws.com%2Fbf%2F03%2F29102d2d1a 39436e8518b709afa6%2Fcousin-chart.jpg
and those two charts https://thegeneticgenealogist.com/2008/12/21/unlocking-the-genealogical-secrets-of-the-x-chromosome/
and place your family on charts it will be easier when looking at it.