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Help with this 1600 cM match

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  • Help with this 1600 cM match

    Shared cMs 1605, longest segment 141, no match on X chromosome. One is male and the other is female. The male has done Y dna testing and we know the surname. The male and female are approximately the same age (within four years of each other) and we know the same number of generations from the MRCA but the tool on Gedmatch has one being the aunt or uncle of the other. This makes no sense at all. Sounds like half siblings to me.

  • #2
    With my half sister, I share:

    1653 cMs
    120 cMs longest
    3 on the X: 13, 37 and 14 cMs

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    • #3
      In the case I mentioned the two individuals are a brother and sister with the same father

      I have a half sister, myself, and we share 1800 cMs with the longest segment 130 cMs. We share the same mother but have different fathers. We don't share any on the X.

      The Relationship Tree Projection tool on Gedmatch isn't accurate. It has my sister and me with an aunt/niece relationship and also in the first example it gave an uncle/niece relationship

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      • #4
        I'm not sure what the problem is. Are they supposed to be full siblings and DNA testing reveals that they are half-siblings?

        A male and female who have the same father but different mothers will not match on the X-chromosome (unless the mothers are related). A son gets a Y-chromosome from his father. A daughter gets an X. A woman has 2 X-chromosomes, one from her mother and one from her father. Usually these will recombine when eggs are formed. Occasionally they don't recombine.

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        • #5
          Gedmatch doesn't say aunt/niece or whatever though. It gives a numerical estimate to MRCA.

          It estimates how many generations to the common ancestor so 1.5 generations for example. It doesn't know the age of the testers.

          Even if Gedmatch DID state aunt/niece, it wouldn't be far off because you share approx 25% of your DNA with an aunt or uncle, and the same amount with a half-sibling.

          Half a generation either way sounds like a good estimate to me.

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          • #6
            Originally posted by MoberlyDrake View Post
            I'm not sure what the problem is. Are they supposed to be full siblings and DNA testing reveals that they are half-siblings?

            A male and female who have the same father but different mothers will not match on the X-chromosome (unless the mothers are related). A son gets a Y-chromosome from his father. A daughter gets an X. A woman has 2 X-chromosomes, one from her mother and one from her father. Usually these will recombine when eggs are formed. Occasionally they don't recombine.
            They are half siblings by our estimation but we are trying to get DNA results to decide between one of two brothers who the father is. However, Gedmatch on the 'tier one' tool has projected two as uncle/niece. I think the system should state the half-sibling option too. It's confusing when they come out and state that they are uncle/niece when a relationship is trying to be proven.

            Originally posted by ltd-jean-pull View Post
            Gedmatch doesn't say aunt/niece or whatever though. It gives a numerical estimate to MRCA.

            It estimates how many generations to the common ancestor so 1.5 generations for example. It doesn't know the age of the testers.

            Even if Gedmatch DID state aunt/niece, it wouldn't be far off because you share approx 25% of your DNA with an aunt or uncle, and the same amount with a half-sibling.

            Half a generation either way sounds like a good estimate to me.
            Actually, Gedmatch has a tier one tool (paid for) which projects the relationship ....not the MRCA distance.

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            • #7
              I'm not sure you will be able to determine who the father is absolutely. My mother has tested at 3 companies. Her grandfather was the son of one of 2 brothers. Judging by circumstances, including age (one brother was 13 or 14 years younger than the other), and by the fact that my mother has 3 matches to the older brother and 2 matches (who are half siblings to each other) to the younger, I think the older is more likely. But I don't think the DNA actually proves it, since one of the matches to the younger brother is closer than the 2 matches to the older brother who tested at the same company.

              I can't compare them all, because the 2 matches to the younger brother will not upload to Gedmatch. And not only will they not upload to Gedmatch, but the 2 matches to the older brother, who tested at Ancestry, won't even reply to emails, much less upload to Gedmatch (and one of them has an incorrect tree), so I can't compare them to all my Mom's cousins who have tested here!
              Last edited by MoberlyDrake; 23 November 2016, 03:30 PM.

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              • #8
                I don't understand your post either. You are all over the place. What exactly are you asking the forum?

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                • #9
                  Originally posted by travers View Post
                  I don't understand your post either. You are all over the place. What exactly are you asking the forum?
                  Travers, I haven't noticed that anyone said they didn't understand my post. I'm sorry you didn't understand.

                  I simply want comments on why 1600 cMs would be automatically considered an Uncle/niece relationship by Gedmatch on their Tier One tool 'Relationship Tree Proection' instead of a half sibling.

                  What is really off with this tool is that I, myself, have a half-sibling (and it is absolutely confirmed) and the tool lists us as Aunt/niece which is totally incorrect. So, it makes me suspect that the tool is useless.

                  I am sorry if I offended you is some way.

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                  • #10
                    Originally posted by Tenn4ever View Post
                    Travers, I haven't noticed that anyone said they didn't understand my post. I'm sorry you didn't understand.

                    I simply want comments on why 1600 cMs would be automatically considered an Uncle/niece relationship by Gedmatch on their Tier One tool 'Relationship Tree Proection' instead of a half sibling.

                    What is really off with this tool is that I, myself, have a half-sibling (and it is absolutely confirmed) and the tool lists us as Aunt/niece which is totally incorrect. So, it makes me suspect that the tool is useless.

                    I am sorry if I offended you is some way.
                    You didn't offend me I was trying to determine what your question is (like MoberlyDrake). You were flip flopping between the what gedmatch predicted or wanting to know which male was the father. As far as the gedmatch prediction I don't have access to it so I can't comment but why don't you ask them (do they have a place for feedback)? It is probably just a prediction and those relationships share the same amount of DNA, you would have more knowledge on the actual situation than gedmatch does so I'm not sure what input anybody here could provide to determine the difference for you. If you know them to be half siblings then that is your answer.

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