Page 1 of 2 12 LastLast
Results 1 to 10 of 18

Thread: Matching on X but not Autosomal?

  1. #1
    Banned
    Posts
    6
    Sex
    Ethnicity
    Welsh/Spanish
    Nationality
    British/Spanish
    Y-DNA
    R1b1a1a2a1a2c
    mtDNA
    H2a2a1f

    Spain Wales England

    Matching on X but not Autosomal?

    On Gedmatch I am matching with a lady with a 43cm chunk on the X Chromosome but absolutely no Autosomal DNA match? Is that possible?
    This is quite a large segment on the X, is this a legitimate match?

    Thanks for reading!

  2. #2
    Registered Users
    Posts
    295
    Sex
    Ethnicity
    Mostly Dutch
    Y-DNA
    R1b-U152 (prob. L2-)
    mtDNA
    W5

    Netherlands
    I think it is possible due to the different inheritance pattern of the X-chromosome; for example, fathers give their X-chromosome unchanged to their daughters. Of course it may or may not recombine when a mother gives hers to her child. There are cases in which someone just inherited an unrecombined X-chromosome from their mother. It is therefore likely that the X-chromosome retains older segments for a longer time.
    Known ancestry (11 gen back):
    Netherlands 74,41%; Germany 8,30%; Belgium 2,15%; France 1,17%; Switzerland 0,29%; England 0,68%;
    Indonesian 5,47%; Dutch East Indies mixed European 1,27%; Ashkenazi 4,69%; Sephardi 1,56%.

  3. #3
    Registered Users
    Posts
    644
    Sex
    Location
    Pittsburgh, PA, USA
    Ethnicity
    German-British-Catalan
    Nationality
    (U.S.) American
    Y-DNA
    R-L1029
    mtDNA
    H1bg

    Germany Palatinate United Kingdom Catalonia France Ireland Switzerland
    Quote Originally Posted by isgaldo View Post
    On Gedmatch I am matching with a lady with a 43cm chunk on the X Chromosome but absolutely no Autosomal DNA match? Is that possible?
    This is quite a large segment on the X, is this a legitimate match?

    Thanks for reading!
    A match of this size is almost always going to be a legitimate match. But as Pylsteen points out, segments on the X chromosome can be handed down by very different paths.

    Here are the actual paths from two different 6th great grandparents to me. Either path could be one by which I received a segment on my X chromosome.

    The first path is from my 6th great grandmother, Marie Anne Catherine Berda dit Picard. Marie Anne Catherine has the distinction of being the most distant known ancestor in my mtDNA line.

    1. 6th great grandmother. Marie Anne Catherine Berda dit Picard.
    2. 5th great grandmother. Angelique Ladner.
    3. 4th great grandmother. Rosalie Fayard.
    4. 3rd great grandmother. Marie-Josephe Ladner.
    5. 2nd great grandmother. Marie Eulalie Ryan.
    6. Great grandmother. Marie Josephine Cannette.
    7. Grandmother. Madeline Mildred Pons.
    8. Mother. Marilyn Pearl Weaver.

    Because these are all female transmissions, they all involved at least the possibility of recombination of the X chromosomes.

    This second path begins with someone whose name I don't yet know, though I known he must have existed. He was the father of my 5th great grandmother, Polly Green. The reason I begin with him is that this line involved the least number of generations in which recombination of the X chromosomes could occur.

    1. 6th great grandfather. Father of Polly Green.
    2. 5th great grandmother. Polly Green.
    3. 4th great grandfather. John E. Bowling.
    4. 3rd great grandmother. Agnes Bowling.
    5. 2nd great grandfather. William Sherman Muncy, Jr.
    6. Great grandmother. Hannah Louise Muncy.
    7. Grandfather. Milford Pearl Weaver.
    8. Mother. Marilyn Pearl Weaver.

    Instead of there being eight generations in which recombination is possible, for this path there are only four. Obviously, that makes it much more likely that a large segment could remain intact from an ancestor at the same distance.

    A cousin whose most recent common ancestor is at the beginning of the first path is likely to share neither a X chromosome match nor an autosomal match -- though either is possible. A cousin whose most recent common ancestor is at the beginning of the second path has a rather good chance of sharing a match on the X chromosome -- but no greater a chance of sharing a match on any of the autosomes.
    Last edited by geebee; 07-23-2017 at 01:35 AM.
    The short explanation of my ancestry is German-British-Catalan, but it actually includes smaller amounts of French, Irish, Swiss, Choctaw and probably Cherokee. My avatar picture is of my father, his father, and his father's father. The baby in the picture is my eldest brother.

    GB

  4. The Following 2 Users Say Thank You to geebee For This Useful Post:

     dp (07-27-2017), Saetro (07-23-2017)

  5. #4
    Registered Users
    Posts
    644
    Sex
    Location
    Pittsburgh, PA, USA
    Ethnicity
    German-British-Catalan
    Nationality
    (U.S.) American
    Y-DNA
    R-L1029
    mtDNA
    H1bg

    Germany Palatinate United Kingdom Catalonia France Ireland Switzerland
    Quote Originally Posted by isgaldo View Post
    On Gedmatch I am matching with a lady with a 43cm chunk on the X Chromosome but absolutely no Autosomal DNA match? Is that possible?
    This is quite a large segment on the X, is this a legitimate match?

    Thanks for reading!
    I believe it's possible to match someone only a single segment this large on an autosome, so it would certainly be possible to match on a single segment this large on the X chromosome.

    I can't confirm this from my own results, but I do match someone on a 35 cM segment which cannot be on the X chromosome. This match is at Ancestry, so I can't actually see where it is, but based on my shared matches it has to be on my maternal grandmother's side. I don't know whether Ancestry includes the X chromosome in determining matching, but even if it does I only match my grandmother on a total of 20 cM on the X chromosome.

    Therefore, to match someone on a single segment of 35 cM on my maternal grandmother's side, the shared segment would have to be on an autosome.
    The short explanation of my ancestry is German-British-Catalan, but it actually includes smaller amounts of French, Irish, Swiss, Choctaw and probably Cherokee. My avatar picture is of my father, his father, and his father's father. The baby in the picture is my eldest brother.

    GB

  6. #5
    Registered Users
    Posts
    521
    Sex
    Location
    USA
    Nationality
    USA
    Y-DNA
    I-FGC24357
    mtDNA
    H5

    United States of America Canada
    Quote Originally Posted by geebee View Post
    I believe it's possible to match someone only a single segment this large on an autosome, so it would certainly be possible to match on a single segment this large on the X chromosome.
    Distant big segment matching, whether it is via autosome or X chromosome, is something that the genetic genealogy mainstream has got completely wrong. Some have said that those matching segments are almost always IBD. If you really examine what is going on from a logic and probability viewpoint, the opposite is true. For a large and distant matching segment to be IBD is a near impossibility.

    Genetic genealogy frequently commits what I call the "chain letter fallacy". Chain letters work if you have an endless supply of people and can find people at each round who have not played before (and won't balk). It is hard to find people who do not have lines back to the same ancestor within the genealogical timeframe. In other words, these big segments are a reconstructed piece of a common ancestor's genome coming from have lines through each parent which go to that ancestor.

    Jack Wyatt
    Last edited by C J Wyatt III; 07-24-2017 at 05:19 PM. Reason: additional thought

  7. #6
    Gold Class Member
    Posts
    382
    Sex
    Location
    Brisbane
    Nationality
    Australian
    Y-DNA
    T-P322
    mtDNA
    H6a1

    Australia Cornwall England Scotland Germany Poland
    Quote Originally Posted by C J Wyatt III View Post
    Distant big segment matching, whether it is via autosome or X chromosome, is something that the genetic genealogy mainstream has got completely wrong. Some have said that those matching segments are almost always IBD. If you really examine what is going on from a logic and probability viewpoint, the opposite is true. For a large and distant matching segment to be IBD is a near impossibility.

    Genetic genealogy frequently commits what I call the "chain letter fallacy". Chain letters work if you have an endless supply of people and can find people at each round who have not played before (and won't balk). It is hard to find people who do not have lines back to the same ancestor within the genealogical timeframe. In other words, these big segments are a reconstructed piece of a common ancestor's genome coming from have lines through each parent which go to that ancestor.
    Jack Wyatt
    Autosomal DNA involves crossovers. These are random events. People are generally not good at handling random events. They like a pattern, and tend to assume that the average applies. That's not too bad for autosomal over 22 chromosomes, especially since the observed variance is not too bad. Even then, some people have noticed that the smaller chromosomes sometimes have no crossovers in one generation.
    The pattern of X inheritance is great for working out who you may and did not inherit that piece of X from.
    Unless your relationship is close, the weird pattern of inheritance with X may cause great frustration.

    Reading people's comments on their experience with the X chromosome suggests that this all or none happens more frequently with the X.
    And then there is the anomalous way it is passed from generation to generation. A woman gets EXACTLY the same X chromosome that her father had.
    A man receives his X chromosome usually as a result of one or more crossover from the two X chromosomes in his mother.
    And then there is an expectation in people that somehow inheritance of the X chromosome is linked to inheritance of autosomal: that if you receive one significant segment on the other 22 and one significant piece on the X that they have been handed down by the same pathway.
    The other thing is a sort of reverse-exceptionalism. We assume that whatever happens to us is the general case and vice versa.
    That really does not work with random events. Sure, if you get enough of them, then the pattern is close to the average; but individual cases may be average or they may be extreme. And anyone who says that everyone they have ever talked to has the average may just never have met the extreme - but it may be the next case they encounter.

    So weird stuff is going on with the X.
    Some of it is already happening with other autosomal, but we often don't notice.
    For both, we need to eventually go from observations rather than models. Models have to make assumptions. They are often based on observations from only limited data.
    If Blaine Bettinger (or someone else) gets around to an X study, we may discover what is really going on.
    We can only find out the average and the variance if we pool real data.

    Or maybe I am misunderstanding your post and there is heaps of data backing your statements.

  8. #7
    Registered Users
    Posts
    521
    Sex
    Location
    USA
    Nationality
    USA
    Y-DNA
    I-FGC24357
    mtDNA
    H5

    United States of America Canada
    Quote Originally Posted by Saetro View Post
    Or maybe I am misunderstanding your post and there is heaps of data backing your statements.
    OK, let's start with my assertion: "For a large and distant matching segment to be IBD is a near impossibility."

    The length of chromosomes in centiMorgans vary, but only five are greater than 200 cM's, so 200 cM will be a good number to use. If you go back six generations. the average decay rate would give you an expected 3.125 cM remaining from the original 200 cM. Of course you cannot expect that will be one segment, but why worry about that detail? if your match is on the same level as you, the person also ends up with an average of 3.125 cM remaining. The catch is, to be a matching segment, it has to line up perfectly with yours. Like I said, a big distant IBD matching segment is near impossible. Do these big segments we see come about from the parents sharing a common ancestor? What other explanations are there?

    Jack

  9. #8
    Registered Users
    Posts
    295
    Sex
    Ethnicity
    Mostly Dutch
    Y-DNA
    R1b-U152 (prob. L2-)
    mtDNA
    W5

    Netherlands
    Yes, it is important to keep in mind that different matching segments with the same person, even if both legitimate, don't have to go back to the same ancestor, certainly not if you share ancestry in the same geographical region, in which case you would share multiple ancestors.
    Known ancestry (11 gen back):
    Netherlands 74,41%; Germany 8,30%; Belgium 2,15%; France 1,17%; Switzerland 0,29%; England 0,68%;
    Indonesian 5,47%; Dutch East Indies mixed European 1,27%; Ashkenazi 4,69%; Sephardi 1,56%.

  10. #9
    Registered Users
    Posts
    644
    Sex
    Location
    Pittsburgh, PA, USA
    Ethnicity
    German-British-Catalan
    Nationality
    (U.S.) American
    Y-DNA
    R-L1029
    mtDNA
    H1bg

    Germany Palatinate United Kingdom Catalonia France Ireland Switzerland
    Quote Originally Posted by C J Wyatt III View Post
    OK, let's start with my assertion: "For a large and distant matching segment to be IBD is a near impossibility."
    Sure, we can start with that. To begin with, you seem to have a fundamental misunderstanding of the word average.

    If I were to tell you that the average height of adult residents of a certain country is 171 centimeters, does that mean I can assume that the next adult I meet from that country will be 171 centimeters? No, of course not. It's possible, but the person could be much taller or much shorter.

    Not only that, but there's an important factor in height that means you aren't typically going to see average height reported this way. What you'll see is not the average height of an adult resident, but of an adult male resident or an adult female resident.

    As it turns out, in the country I was referring to, the average height for a man is given as 179 centimeters, and the average height for a woman is 163 centimeters. There's a 16 centimeter difference in these two averages -- or about 6 inches. So if I guess that the next person I see will be 171 centimeters and the person is female, I'm likely to have guessed too high -- although since it's an average, that particular woman might well be much taller. Or if the person is a man, the guess of 171 centimeters will likely be a bit low. But again, because it's an average, that particular man might be even shorter; or he could be much, much taller.

    The same thing applies to recombination. In fact, here the gender difference is even more significant than in height. The average crossover rate for men is much lower than it is for women. What does this mean? Well, for one thing, it means that when we're told the length of chromosomes in centimorgans, that number represents an average -- but it's an average that doesn't exist in the real world. To obtain it, you have to average the crossover rate for men and women together. But no one is the offspring of two generic parents. Everyone is the offspring of a male and a female, and these two will probably have very different crossover rates. (One study found an average of 42 crossovers per recombination event in women, versus 28 in men.)

    If you have 42 crossovers spread over 23 chromosomes, it would be possible for a crossover to occur on every chromosome, and for a second crossover to occur on almost every chromosome. But, 28 crossovers only allows for a second crossover on a few chromosomes.

    In reality, of course, in both cases a few chromosomes may escape recombination altogether (that is, have no crossovers). Other chromosomes may have more than two crossovers.

    This isn't just hypothetical, it's what people have actually been able to observe. For example, I can tell by comparing my father's genome to my daughter's that I passed on to her:

    • 8 chromosomes with no crossovers (7, 9, 15, 17, 18, 21, 22, X)
    • 10 chromosomes with 1 crossover each (1, 4, 8, 10, 11, 12, 13, 16, 19, 20)
    • 3 chromosomes with 2 crossovers each (5, 6, 14)
    • 1 chromosome with 3 crossovers (2)
    • 1 chromosome with 4 crossovers (3)


    This is a total of 25 crossovers -- so not far from the average of 28.

    But the important thing to realize about the gender difference in crossover rates is that it doesn't simply have implications for a single recombination event. It also affects entire series of recombination events.

    Consider your example of an ancestor 6 generations ago. If that ancestor and all five of the descendants who are also your ancestors happen to all be male, then that makes for many fewer total crossovers in the six generations. The number in this case -- assuming each recombination event involves the average number of crossovers -- is 168. That actually yields an average segment size not of 3.125 cM, but a little over 21 cM.

    At the other extreme, with the line of all females you get 6*47. That yields a total of 282 crossovers, or something more like 12.5 cM. (Still quite a bit more than 3.125 cM.)

    But once again, these are averages. Why do you believe that in every transmission, the crossovers will manage to arrange themselves to get averaged-sized segments? There will be an average segment size only because no matter what size each segment is, the total length of all the segments can be summed and averaged. That doesn't mean that any, or even most, segments will actually be this average.

    Here's another list for you. It shows what percentage of each chromosome my daughter inherited from my father.

    • chromosome 1: 82%
    • chromosome 2: 29%
    • chromosome 3: 39%
    • chromosome 4: 55%
    • chromosome 5: 33%
    • chromosome 6: 21%
    • chromosome 7: 0%
    • chromosome 8: 16%
    • chromosome 9: 100%
    • chromosome 10: 96%
    • chromosome 11: 78%
    • chromosome 12: 35%
    • chromosome 13: 87%
    • chromosome 14: 53%
    • chromosome 15: 0%
    • chromosome 16: 71%
    • chromosome 17: 0%
    • chromosome 18: 0%
    • chromosome 19: 98%
    • chromosome 20: 79%
    • chromosome 21: 100%
    • chromosome 22: 0%
    • X chromosome: 0%


    The point of the above list is mainly to show how rarely crossovers resulted in an even division of segments. Actually, only twice -- on chromosomes 4 and 14 -- did my daughter inherited about half of the DNA on the chromosome from her grandfather. In all other cases, the division was more lopsided.

    Now this is just one example, and I have no way of knowing how typical it is. But it should serve to show that the mechanism of recombination can result in both very large segments and very small segments. Because crossovers occur more-or-less randomly*, they can't be relied on to come up with "average" sized segments. And while over a series of recombination events in a given line this mechanism may tend to even things out, it definitely does not have to do so.

    To give one last example of just how large a segment can persist for a surprisingly long time, a 2nd cousin of mine recently uploaded his DNA file to GEDmatch. This has allowed me to compare not only the segments I share with my cousin, but the segments my siblings share. One of my brothers shares an 80.5 cM segment on chromosome 20 with this cousin. This represents 70% of the entire chromosome, when the closest common ancestors are great grandparents.

    And, no, it doesn't reflect the relatedness of either my maternal grandparents or my parents. My grandfather's ancestry was primarily from Virginia and Kentucky; my grandmother had three immigrant grandparents, and her non-immigrant grandparent was from the Gulf Coast of Mississippi. My father's ancestry is all from Pennsylvania since colonial times. It simply shows that very large segments can be passed on over several generations.

    And if in three generations (great grandparents, grandparents, parents) a segment that began as 108 cM-long chromosome only "decayed" to 80.5 cM, it doesn't seem likely that survival of a "big" distant segment in just a few more generations is "near impossible".
    Last edited by geebee; 07-26-2017 at 06:41 AM.
    The short explanation of my ancestry is German-British-Catalan, but it actually includes smaller amounts of French, Irish, Swiss, Choctaw and probably Cherokee. My avatar picture is of my father, his father, and his father's father. The baby in the picture is my eldest brother.

    GB

  11. The Following User Says Thank You to geebee For This Useful Post:

     Pylsteen (07-26-2017)

  12. #10
    Gold Class Member
    Posts
    382
    Sex
    Location
    Brisbane
    Nationality
    Australian
    Y-DNA
    T-P322
    mtDNA
    H6a1

    Australia Cornwall England Scotland Germany Poland
    Quote Originally Posted by C J Wyatt III View Post
    OK, let's start with my assertion: "For a large and distant matching segment to be IBD is a near impossibility."
    The length of chromosomes in centiMorgans vary, but only five are greater than 200 cM's, so 200 cM will be a good number to use. If you go back six generations. the average decay rate would give you an expected 3.125 cM remaining from the original 200 cM. Of course you cannot expect that will be one segment, but why worry about that detail? if your match is on the same level as you, the person also ends up with an average of 3.125 cM remaining. The catch is, to be a matching segment, it has to line up perfectly with yours. Like I said, a big distant IBD matching segment is near impossible. Do these big segments we see come about from the parents sharing a common ancestor? What other explanations are there?
    Jack
    geebee in Post #9 above has demonstrated that averages DO NOT APPLY, necessarily, to single transfer events like the transfer from one person to another of a single chromosome. Even over 2 generations from his father to his daughter there are 4 chromosomes that have ZERO transmitted.
    And if the average applied, then we would not have ancestors dropping out from our matches after a few generations. The matches would just get smaller.
    So, if we get zero from some transfers, then we don't just have no chromosome. We get MORE from someone else, often as a longer segment.
    Crossovers are random events. Sure the average describes what happens over large populations, but it is the spread of results that matter.
    Blaine Bettinger's tables of accumulated actual events shows how the total DNA inherited from one individual can be zero with a relationship of 2C1R.
    http://thegeneticgenealogist.com/wp-...-UPDATED-1.pdf

    So if some segments have zero inheritance, others are bigger.
    Yes, they will usually become trimmed or lost by later crossovers, but just occasionally they survive for several generations longer than expected.
    A very few will come from what we would normally consider a long way back.
    It's rare, but it happens.
    It's not the average, alone, that describes behavior of segments, but the average plus variance - the spread.
    Last edited by Saetro; 07-26-2017 at 08:59 PM.

Page 1 of 2 12 LastLast

Similar Threads

  1. DNA Matching
    By AntG in forum Living DNA
    Replies: 2
    Last Post: 02-03-2017, 07:02 PM
  2. Matching on gedmatch?
    By Deftextra in forum Autosomal (auDNA)
    Replies: 16
    Last Post: 03-14-2016, 12:43 AM
  3. STR matching for R people
    By Eochaidh in forum R
    Replies: 17
    Last Post: 01-01-2016, 09:35 PM
  4. Usefulness of Higher Density SNP Testing in Autosomal Matching
    By JamesKane in forum Autosomal (auDNA)
    Replies: 1
    Last Post: 01-03-2014, 06:26 PM
  5. Help with Y-DNA not matching my Surname
    By migoblu in forum R1b General
    Replies: 3
    Last Post: 10-13-2013, 06:21 PM

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •