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  • Are these half cousins?

    Hello, all! I have a question regarding 2nd cousins and how much DNA they are supposed to share.

    There are some cousins on my mom's side who seemed to share less with me than I figured they would. But being that they are all 2nd cousins 1x removed to me, I didn't put much thought into it. Recently, I got my mom tested and surprisingly, they still come back sharing a lot less than I had thought they would.

    2nd Cousin #1 - 200 cm
    2nd Cousin #2 - 138 cm
    2nd Cousin #3 - 120 cm
    2nd Cousin #4 - 201 cm
    2nd Cousin #5 - 63 cm
    2nd Cousin #6 - 117 cm (could be 2nd 1x removed instead but not sure)

    Cousins 2, 3, and 4 are all siblings and Cousins 1 and 5 are first cousins.

    This surprised me because 2nd cousins on my mom's paternal line share at least double this amount with her. Also, I did a bit more digging and found that of my mom's grandma's siblings (10 children total including her), one of the male descendants tested and their paternal haplogroup matched others of the same surname in a FTDNA project - Hall. But 2nd Cousin #6 is also a male descendant (from the youngest son, only two years older than my mom's grandma who was the youngest child) and his paternal haplogroup was completely different. That suggests to me that he didn't share the same Hall father as the others.

    To keep up with all of this, I've been tracking it all through DNAPainter. Through this, I noticed that most of these 2nd cousins only match Greenwood cousins (my mom's great-grandma's side). And even the male descendant from the youngest son only matches Greenwood cousins.

    I've even searched for Hall cousins through my great-grandma's dad's side but none have come up. Alternately, I've even searched for unknown close cousins to point to a biological father but still, nothing.

    With that being said, does this point to a half-cousin relationship for my mom and her 2nd cousins? And in turn, a half-sibling relationship for her grandmother and her own siblings?

    I'm not really sure what to make of all this. Any help would be appreciated.

  • #2
    Have you used DNA Painter | Shared cM Project 4.0 tool v4 with relationship probabilities

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    • #3
      I did try that out! Almost every single cousin came up as a 45%-52% chance of being a half second-cousin. It seems to point to this in my opinion. But I wasn't totally sure since I'm not completely familiar with the shared DNA aspect of genealogy.

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      • #4
        My mistake - I wrote different paternal haplogroups but I've checked again and this is false. They still share the same haplogroup, only different sub-clades. So apparently, still the same Hall father.

        Although, I did have a thought - could it be possible that my great-grandma was being raised by her "mom" but was actually a grandchild to her? My great-grandma's mom was already 6 months pregnant when she married her Hall husband and I highly suspect he was not the father of that eldest child, probably more like an arranged marriage since he was so much older than her. Could it be possible that my great-grandma was the daughter of this child?

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        • #5
          Here are some numbers in case you don't already have them. On average, two second cousins share 212 cM. A second cousin, once removed or a half-second cousin would share half of that.

          In my own family, there's a half-second cousin, and five of us are related to him in the same way, but the shared cM in Family Finder are 91, 121, 128, 145 and 151, and in GEDmatch (using more than one result the cousin has posted) 73, 82, 105, 126, 131, 143, and 171. So our numbers vary from the 106 cM average by -31% to +61%.

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          • #6
            Originally posted by QueenofHearts96 View Post
            My mistake - I wrote different paternal haplogroups but I've checked again and this is false. They still share the same haplogroup, only different sub-clades. So apparently, still the same Hall father.

            Although, I did have a thought - could it be possible that my great-grandma was being raised by her "mom" but was actually a grandchild to her? My great-grandma's mom was already 6 months pregnant when she married her Hall husband and I highly suspect he was not the father of that eldest child, probably more like an arranged marriage since he was so much older than her. Could it be possible that my great-grandma was the daughter of this child?
            Its great you have tested the paternal side, because for such a complex case, this is the only solid proof. What do you mean by different subclade? If the subclade is different, unless its just one or maximally 2 SNPs difference, this suggests still a different father: Did you check on blocktree how many SNPs are different and how do they compare on the STR test?

            I'm in a similar situation with a supposed full 2nd cousin at 136 cM total, including small segments below 5 cM, largest block is 51 cM. The predicted range being 2nd Cousin - 3rd Cousin.

            A factor of additional uncertainty comes from the fact that I tested on the new FTDNA chip just recently, while she tested on the old, years ago. So the overlap might not be perfect for the comparison and from my experience on Gedmatch, even though I couldn't check her data there, this matters. I also compared her with another upload, the data was slightly different, but the same range of about 130 cM in total, which is closer to a half second cousin, but still in the possible good range for a full 2nd cousin as well. I tried to find direct matches for that branch of my family as well, but while I found a couple of possible ones, with the same villages and surnames, none is 100 percent so far. This may be the case because this particular ancestral group is severely undertested, as all my potential matches from the region agreed upon. Even people with much more ancestry from these places get only a handful of matches at best.
            Last edited by Börum; 26 April 2021, 09:12 AM.

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            • #7
              Originally posted by QueenofHearts96 View Post
              My mistake - I wrote different paternal haplogroups but I've checked again and this is false. They still share the same haplogroup, only different sub-clades. So apparently, still the same Hall father.
              Do you mean that one is in a subclade of the other's haplogroup, so within the same branch? Could you post the subclades of both, so we can understand better? Did these men both test at FTDNA to get Y-DNA results? Do you know which tests they had done?

              Sometimes there is a different subclade shown because further testing has been done by one and not the other, but they are in the path of the same main branch. If the other did further testing, you could see if they were in the same subclade.

              You have found a male descendant of one of your great-grandmother's siblings from the Hall father. If your 2nd great-grandmother (who married Mr. Hall when 6 mos. pregnant) went on to have nine other children by Mr. Hall, including your grandmother and her male siblings, the terminal SNP of the male siblings' sons and their male descendants should be the same, with perhaps some genetic distance in STRs (Y-37, Y-67, etc.). But they may not have done SNP testing; if not, the predicted haplogroups from STR testing should be in the path of the same branch.

              Originally posted by QueenofHearts96 View Post
              Although, I did have a thought - could it be possible that my great-grandma was being raised by her "mom" but was actually a grandchild to her? My great-grandma's mom was already 6 months pregnant when she married her Hall husband and I highly suspect he was not the father of that eldest child, probably more like an arranged marriage since he was so much older than her. Could it be possible that my great-grandma was the daughter of this child?
              Regarding if your great-grandmother could have been the daughter of the eldest child, and that eldest child may not have been a child of Mr. Hall, anything is possible. Was the eldest child (presuming a daughter) old enough to have children when your great-grandmother was born? It seems very likely, with 9 siblings born after the eldest, and your g-grandmother one of the youngest. If your great-grandmother was indeed the child of the eldest daughter, she would have had a different father, unless it was a case of incest.

              Having a different father would explain the half-cousin possibilities; the one common ancestor would be the mother of your great-grandmother (2nd g-grand). I'm not sure how the Greenwood cousins fit in; you said your mother's great-grandmother's side, so are they in your mother's direct maternal line, via one of her siblings, or descended via siblings of her mother or grandmother? Your great-grandmother's mtDNA haplogroup would still be the same, even if she was the daughter of the eldest child, if that child was a female.

              Out of curiosity, for autosomal matches with these 2nd cousins: have you seen any matching segments on the X-chromosome with any of them, particularly to your mother? If so, what size were they?

              I hope all that was not too confusing!

              Comment


              • #8
                An important component in working out the relationships from the genetic data is to make ALL of the comparisons, each of those kits with every other related kit. In this way, you can work out all of the possibilities -- not just their relationships to you, but also all of their relationships with each other. You should also verify the existence of half-match and full-match segments and make sure that individual matching segments really do triangulate (or not) in a way that is consistent with the relationships you deduce from other evidence. Adding other relatives to the mix, if possible, can also help you find the correct solution -- the more relatives who are tested and whose kits can be compared directly, the better!

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                • #9
                  Originally posted by stennor View Post
                  Here are some numbers in case you don't already have them. On average, two second cousins share 212 cM. A second cousin, once removed or a half-second cousin would share half of that.

                  In my own family, there's a half-second cousin, and five of us are related to him in the same way, but the shared cM in Family Finder are 91, 121, 128, 145 and 151, and in GEDmatch (using more than one result the cousin has posted) 73, 82, 105, 126, 131, 143, and 171. So our numbers vary from the 106 cM average by -31% to +61%.
                  Hm, that actually sounds about right to what my mom shares with her 2nd cousins. At first, I thought I was reading it all wrong and maybe I had misinterpreted but the numbers don't seem to add up to be a full second-cousin.

                  Originally posted by Börum View Post

                  Its great you have tested the paternal side, because for such a complex case, this is the only solid proof. What do you mean by different subclade? If the subclade is different, unless its just one or maximally 2 SNPs difference, this suggests still a different father: Did you check on blocktree how many SNPs are different and how do they compare on the STR test?
                  Originally posted by KATM View Post
                  Do you mean that one is in a subclade of the other's haplogroup, so within the same branch? Could you post the subclades of both, so we can understand better? Did these men both test at FTDNA to get Y-DNA results? Do you know which tests they had done?

                  Sometimes there is a different subclade shown because further testing has been done by one and not the other, but they are in the path of the same main branch. If the other did further testing, you could see if they were in the same subclade.

                  You have found a male descendant of one of your great-grandmother's siblings from the Hall father. If your 2nd great-grandmother (who married Mr. Hall when 6 mos. pregnant) went on to have nine other children by Mr. Hall, including your grandmother and her male siblings, the terminal SNP of the male siblings' sons and their male descendants should be the same, with perhaps some genetic distance in STRs (Y-37, Y-67, etc.). But they may not have done SNP testing; if not, the predicted haplogroups from STR testing should be in the path of the same branch.

                  Regarding if your great-grandmother could have been the daughter of the eldest child, and that eldest child may not have been a child of Mr. Hall, anything is possible. Was the eldest child (presuming a daughter) old enough to have children when your great-grandmother was born? It seems very likely, with 9 siblings born after the eldest, and your g-grandmother one of the youngest. If your great-grandmother was indeed the child of the eldest daughter, she would have had a different father, unless it was a case of incest.

                  Having a different father would explain the half-cousin possibilities; the one common ancestor would be the mother of your great-grandmother (2nd g-grand). I'm not sure how the Greenwood cousins fit in; you said your mother's great-grandmother's side, so are they in your mother's direct maternal line, via one of her siblings, or descended via siblings of her mother or grandmother? Your great-grandmother's mtDNA haplogroup would still be the same, even if she was the daughter of the eldest child, if that child was a female.

                  Out of curiosity, for autosomal matches with these 2nd cousins: have you seen any matching segments on the X-chromosome with any of them, particularly to your mother? If so, what size were they?

                  I hope all that was not too confusing!

                  Well, one of the descendants of one of my great-grandma's brothers tested with FTDNA (unsure of the identity since he's only listed by kit number under the Hall group) and he come back as I-FT344905. The other cousin descended from the youngest son only a couple years older than my great-grandma (either second cousin or second cousin 1xremoved, I'm not sure) tested on 23andMe and he come back as I-PF4135.

                  Someone on another forum told me that this meant they were still related through the father which is why I had mentioned my suspicions as being false in a later post.

                  Yes, the eldest daughter was 22 years old when my great-grandma was born. That's why it would make a lot of sense for the difference in DNA shared but still have matches from the mother's side. Because of sharing the maternal grandmother. Yes, my great-grandma's mom was a Greenwood.

                  Hm, I have not actually! I'll check that though and get back to you. From memory, I don't think there was that many of them who matched that much on the X chromosome. Again, found that kind of odd LOL.
                  Last edited by QueenofHearts96; 28 April 2021, 05:30 PM.

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                  • #10
                    Originally posted by KATM View Post

                    Out of curiosity, for autosomal matches with these 2nd cousins: have you seen any matching segments on the X-chromosome with any of them, particularly to your mother? If so, what size were they?
                    Just checked the X chromosome matches for my mom's cousins.

                    One is a 2nd cousin 1x removed who matches 63.1 cm on the X. But I was shocked to find that when I checked, none of the other second cousins matched any X dna whatsoever. Is that normal? LOL

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                    • #11
                      Also, just got an update on the match that is a descendant of the youngest brother and he is indeed a second cousin and not 1x removed like I had thought. Bad news is he only shares 117 cm with my mom. And I'm not sure that's high enough to count as a full second cousin? Hm...

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                      • #12
                        The Shared cM Project at DNA Painter shows a 10% chance of sharing 117 cM with a full second cousin.

                        Here's a page that includes the DNA Detectives Autosomal Statistics Chart with its explanation page, as well as several other useful charts, in one .pdf (called "A Selection of Useful Statistics" compiled by Michelle Patient). The other charts are from Blaine Bettinger and ISOGG, and there are links to the originals there.

                        The DNA Detective's chart includes 117 cM in Groups E and F, which includes:
                        • (for group E, 75-360 cM shared) Second cousin, first cousin twice removed, half first cousin once removed
                        • (for group F, 30-215 cM shared) Second cousin once removed, half second cousin, first cousin three times removed, and half first cousin twice removed.
                        Perhaps the youngest brother is a second cousin on paper, but might be a half second cousin?

                        For X-matching, I'm not aware of any statistics of how the X is shared for different levels of relationships. I checked the kits I manage, among which are those for a brother and sister. They match two people who are known second cousins to them, but neither match on the X chromosome. Only the sister ("A") matches one male first cousin once removed ("B") on the X, on one segment of 13.26 cM and one segment of 6.28 cM (so this shared X came from A's paternal X, as they are related through her father and the male B's maternal line; B's maternal grandmother was a sister to A's father). The X segments they share are not adjacent, but are very likely IBD, not IBS, at that relationship level of 1C1R.

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                        • #13
                          Originally posted by KATM View Post
                          The Shared cM Project at DNA Painter shows a 10% chance of sharing 117 cM with a full second cousin.

                          Here's a page that includes the DNA Detectives Autosomal Statistics Chart with its explanation page, as well as several other useful charts, in one .pdf (called "A Selection of Useful Statistics" compiled by Michelle Patient). The other charts are from Blaine Bettinger and ISOGG, and there are links to the originals there.

                          The DNA Detective's chart includes 117 cM in Groups E and F, which includes:
                          • (for group E, 75-360 cM shared) Second cousin, first cousin twice removed, half first cousin once removed
                          • (for group F, 30-215 cM shared) Second cousin once removed, half second cousin, first cousin three times removed, and half first cousin twice removed.
                          Perhaps the youngest brother is a second cousin on paper, but might be a half second cousin?

                          For X-matching, I'm not aware of any statistics of how the X is shared for different levels of relationships. I checked the kits I manage, among which are those for a brother and sister. They match two people who are known second cousins to them, but neither match on the X chromosome. Only the sister ("A") matches one male first cousin once removed ("B") on the X, on one segment of 13.26 cM and one segment of 6.28 cM (so this shared X came from A's paternal X, as they are related through her father and the male B's maternal line; B's maternal grandmother was a sister to A's father). The X segments they share are not adjacent, but are very likely IBD, not IBS, at that relationship level of 1C1R.
                          Oh wow, that's a really low percentage! Hm, well I had been suspecting that they were only half second-cousins and not full second-cousins.

                          And based on those percentages you shared, that deduction seems about right. That's what I think, too. Now I guess that only leaves me with two possible options - either my great-grandma was the daughter of the eldest child as was the youngest brother (with different fathers) or she just had a different father from the rest of the Hall children. I guess the only thing that could point to that deduction would be the haplogroups to see if the youngest brother's father was the Hall man.

                          Does anyone know anything about the two I mentioned, I-FT344905 and I-PF4135? I'm not fully versed in haplogroups and how they work to know if this would be from different dads or just a mutation down the line.

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                          • #14
                            Originally posted by QueenofHearts96 View Post
                            Does anyone know anything about the two I mentioned, I-FT344905 and I-PF4135? I'm not fully versed in haplogroups and how they work to know if this would be from different dads or just a mutation down the line.
                            You can use FTDNA's Y-DNA Haplotree (link is at bottom of the FTDNA home page), and search by each branch's name. I did, and it turns out that I-FT344905 is in a subclade beneath I-PF4135:

                            I-PF4135_to_I-FT344905.png
                            The path is I-PF4135 > I-Y91501 > I-A11374 > I-Z45261 > I-FT344905. This indicates that one of the men has tested further than the other man, since one subclade is a descendant of the other.
                            Last edited by KATM; 29 April 2021, 01:14 PM.

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                            • #15
                              Originally posted by KATM View Post

                              You can use FTDNA's Y-DNA Haplotree (link is at bottom of the FTDNA home page), and search by each branch's name. I did, and it turns out that I-FT344905 is in a subclade beneath I-PF4135:

                              I-PF4135_to_I-FT344905.png
                              The path is I-PF4135 > I-Y91501 > I-A11374 > I-Z45261 > I-FT344905. This indicates that one of the men has tested further than the other man, since one subclade is a descendant of the other.
                              Oh, okay! So that's actually not that far off then. So does that mean the Hall man fathered the older son as well as the younger one? Sorry, the DNA aspect of genealogy is still kind of new to me LOL.

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