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What's the longest surviving large segment you've seen?

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  • hansonrf
    replied
    Originally posted by sjadelson View Post
    Hi Bob,

    Are these values documented somewhere?

    In my case - the match for which I started this thread - chr 1 contains three sizable chunks: the massive 49cM one, a 13cM one, a 5.01cM, and finally a small 1.06cM. That's 59% of the total 5+cM segment shared, and 42% of the total shared.
    Sure are... Rutgers at:

    http://compgen.rutgers.edu/RutgersMap/MapBrowser.aspx
    Attached Files

    Leave a comment:


  • sjadelson
    replied
    Originally posted by hansonrf View Post
    If you look closely at the statistics and then the variations we observe, 22 cM is not that unexpected. The average size of a segment surviving that long would be 8-10 cM. Twice+ average is reasonable variation. We see 3-4x regularly.

    I would be curious if these long segments can be traced to predominantly male lineage or predominantly female lineage, or a truly mixed bag. The reason is that recent data shows large differences in meiotic crossover rates between males and females and chromosome-to-chromosome; males crossover less, females more [55%]. The ratio ranges from 17% [chr 20] to 80% [chr 8] more for females. [male lineage would thus have longer surviving segments]
    Hi Bob,

    Are these values documented somewhere?

    In my case - the match for which I started this thread - chr 1 contains three sizable chunks: the massive 49cM one, a 13cM one, a 5.01cM, and finally a small 1.06cM. That's 59% of the total 5+cM segment shared, and 42% of the total shared.

    Leave a comment:


  • hansonrf
    replied
    If you look closely at the statistics and then the variations we observe, 22 cM is not that unexpected. The average size of a segment surviving that long would be 8-10 cM. Twice+ average is reasonable variation. We see 3-4x regularly.

    I would be curious if these long segments can be traced to predominantly male lineage or predominantly female lineage, or a truly mixed bag. The reason is that recent data shows large differences in meiotic crossover rates between males and females and chromosome-to-chromosome; males crossover less, females more [55%]. The ratio ranges from 17% [chr 20] to 80% [chr 8] more for females. [male lineage would thus have longer surviving segments]

    FWIW...

    Bob H.


    Originally posted by Frederator View Post
    Those stories are pretty impressive.

    I have a story, but it's more impressive on grounds of extreme age of a segment, versus sheer size alone. Though in context, I think 22 cM is fairly large for a segment 400 years old.

    I have a mass of 5 people who appear to overlap one another on chromsome #9. No magic bullets to identify the specific shared ancestors, but the pattern of people who are "In Common With" one another makes the broad outline pretty clear: I relate to 3 of them from one of my maternal lines from County Cork, and I relate to the other 2 from one of my paternal lines from the north of Ireland. I think County Down.

    The Down bunch share a common ancestor with each other born in 1640 and died in Virginia colony. None of my ancestors were in America before 1850, and none ever lived in Virginia. There is no record of backmigration in either family.

    I'm thinking our common ancestor could not possibly be any later than 1600. I guess that would make us round about 7th cousins, bare minimum.

    I have another story, but I think it is less clear cut.

    In that case, two of my matches claim a common ancestor born about 1610. One of matches is a projected 3rd cousin to me with a largest segment of 30 cM.

    I believe I actually descend from the same common ancestor identified between those two matches, but there is room for doubt. The segments they share with me do not overlap, although they do have many matches in common between each other whose common ancestors definitely came from the region in question (i.e., County Antrim).
    Last edited by hansonrf; 7 October 2013, 10:15 AM. Reason: add a thought

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  • Frederator
    replied
    Those stories are pretty impressive.

    I have a story, but it's more impressive on grounds of extreme age of a segment, versus sheer size alone. Though in context, I think 22 cM is fairly large for a segment 400 years old.

    I have a mass of 5 people who appear to overlap one another on chromsome #9. No magic bullets to identify the specific shared ancestors, but the pattern of people who are "In Common With" one another makes the broad outline pretty clear: I relate to 3 of them from one of my maternal lines from County Cork, and I relate to the other 2 from one of my paternal lines from the north of Ireland. I think County Down.

    The Down bunch share a common ancestor with each other born in 1640 and died in Virginia colony. None of my ancestors were in America before 1850, and none ever lived in Virginia. There is no record of backmigration in either family.

    I'm thinking our common ancestor could not possibly be any later than 1600. I guess that would make us round about 7th cousins, bare minimum.

    I have another story, but I think it is less clear cut.

    In that case, two of my matches claim a common ancestor born about 1610. One of matches is a projected 3rd cousin to me with a largest segment of 30 cM.

    I believe I actually descend from the same common ancestor identified between those two matches, but there is room for doubt. The segments they share with me do not overlap, although they do have many matches in common between each other whose common ancestors definitely came from the region in question (i.e., County Antrim).
    Last edited by Frederator; 2 October 2013, 02:40 PM.

    Leave a comment:


  • Ann Turner
    replied
    The entire length of chromosome 4 (190 Mb) was inherited by me, my sister, and my uncle (thus four transmission events). Virtually all (4 to 186 Mb) was inherited by my uncle's grandson (so possibly one more).

    Leave a comment:


  • blejerh
    replied
    My third cousin and his daughter share a longest segment of 48.38 cM with me. Our family lived in a small village (700 Jews) where at the time when the village was largest, people with our surname alone were about a 1/8 of the population (80 people) and we lived there 100 - 150 years and likely had several shared ancestors.

    Our 6th cousin on this branch shares 31.x cM with me.

    Leave a comment:


  • nwgen
    replied
    Originally posted by MMaddi View Post
    Those aren't my full marker values. The ysearch account with all my 111 marker results is 6M79M.

    The account you're referring to, 2NB94, only has my results for the 16 slowest markers among the first 37. It's not that hard to match those 16 markers. There are 39 exact matches to 2NB94.
    yep

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  • MMaddi
    replied
    Originally posted by nwgen View Post
    The match is in Ysearch to user ID 2NB94. Very distant.....
    Those aren't my full marker values. The ysearch account with all my 111 marker results is 6M79M.

    The account you're referring to, 2NB94, only has my results for the 16 slowest markers among the first 37. It's not that hard to match those 16 markers. There are 39 exact matches to 2NB94.

    Leave a comment:


  • nwgen
    replied
    Originally posted by MMaddi View Post
    You're saying that I'm a yDNA match along your uncle's paternal line? This is news to me, since I have only one match at the 12, 25, 37 and 67 marker levels in the FTDNA database. Is your uncle's paternal line Italian?
    The match is in Ysearch to user ID 2NB94. Very distant.....

    Leave a comment:


  • nwgen
    replied
    Originally posted by Javelin View Post
    I've looked at all my various tested known cousins and there are no cases precisely like this. I even have a set of first cousins three times removed, and they have way more blocks than this though none as long.

    This seems most similar among my kits to a set of second cousins twice removed, who share a largest block of 44 cM and 11,700 SNPs with no additional blocks over 5 cM. Thus I am going to guess your match is something like a second cousin twice removed or a third cousin once removed.
    Anything is possible. My next largest is 41cM and 8600 SNPs.

    Leave a comment:


  • 1_mke
    replied
    I've mentioned this here before but...

    Not sure of the relationship since both sides at the root of this comparison were adopted but check out

    http://ww2.gedmatch.com:8006/autosom...isplay+Results

    The same 30cM segment is present in three generations of the other line (grandmother, mother, daughter) on the other line and two on mine (Mom, me/son). My brother only has a small portion of this segment so it isn't totally persistent.

    The earliest two (my mom, grandmother of other line) have one additional 5cM segment in common so maybe we're getting into the third or fourth cousin range there?

    Leave a comment:


  • Javelin
    replied
    Originally posted by nwgen View Post
    84 cM total. 1 block over 5cM and it is 66.5 cM and 16000 SNPs.
    I've looked at all my various tested known cousins and there are no cases precisely like this. I even have a set of first cousins three times removed, and they have way more blocks than this though none as long.

    This seems most similar among my kits to a set of second cousins twice removed, who share a largest block of 44 cM and 11,700 SNPs with no additional blocks over 5 cM. Thus I am going to guess your match is something like a second cousin twice removed or a third cousin once removed.

    Leave a comment:


  • MMaddi
    replied
    Originally posted by nwgen View Post
    Ironically, I'm pretty certain this match is along my uncle's paternal line. You are a YDNA match along this same line, though not a close match. Six degrees of separation....
    You're saying that I'm a yDNA match along your uncle's paternal line? This is news to me, since I have only one match at the 12, 25, 37 and 67 marker levels in the FTDNA database. Is your uncle's paternal line Italian?

    Leave a comment:


  • nwgen
    replied
    Originally posted by MMaddi View Post

    This seems very unusual, especially since the relationship is 4th cousin or more distant. It almost defies the laws of probability involved in DNA recombination.
    Indeed it is very large and unusual. Ironically, I'm pretty certain this match is along my uncle's paternal line. You are a YDNA match along this same line, though not a close match. Six degrees of separation....

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  • MMaddi
    replied
    Originally posted by nwgen View Post
    84 cM total. 1 block over 5cM and it is 66.5 cM and 16000 SNPs.
    This match is not of the same type as the ones sjadelson and I have posted about. There's only one block above 5 cM and it's very large. I think it's safe to say that 2nd and 3rd cousins almost always share more than one segment above 5 cM.

    This seems very unusual, especially since the relationship is 4th cousin or more distant. It almost defies the laws of probability involved in DNA recombination.

    Leave a comment:

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