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Proving babies switched, how to prove, advice requested

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  • Proving babies switched, how to prove, advice requested

    Hello,
    I have recently added 4 ladies to my my tree. Three are sisters and the 4th is a 1st cousin to the three sisters, so they say. When I view their shared cM with me, the 3 sisters have a cM range of 111 to 181, while the 4th lady has only 52 cM shared with me. Here is the intriguing point: their reported grandfather had a 1st cousin born the same year, 2 or 3 months apart, in the same town and of the same first and last names. These are two men, as they spent their adult lives in different cities with different wives.
    I would speculate that the 3 sisters are my 3rd cousins, based on the share cM and that the 4th lady is a 5th cousin, because of my fully researched tree.
    I do not yet have the shared cM between them and other members of the tree. The tree is suggesting that my hypothesis is correct. An alternative hypothesis is that the wife of the grandfather of the four ladies had an evening with his 1st cousin, there by producing a son, a half sibling, and generating a 3rd cousin match to me.
    I hope to have been clear enough for comments. I've view the cM calculator.
    Thanks in advance, James O'Donnell

  • #2
    The range you report for the 3 sisters matching with you is a bit higher than the normal range for 3rd cousins (95 percent range for 3rd cousins reported on the widely cited and highly recommended "DNA Detectives Autosomal Statistics Chart" is 0-109 cM). Even disregarding that, however, the figures don't allow you to distinguish relationships with the degree of precision that you need in this situation. For example, the 3 sisters could equally well fit the normal ranges as your 2nd cousins, half 1st cousins once removed, half 2nd cousins, etc., all the way out to (maybe, unusually) 3rd cousins or 2nd cousins twice removed. In other words, I don't think you have enough genetic evidence yet to support any particular family tree to the exclusion of all other possibilities. You definitely need to know the cM for the matches of each of the 3 sisters with their 1st cousin, and if possible, also whether there is a strong X match for any of these matches. Also shared cM (autosomal and X) of these 4 women with anyone else in this kindred who has already been tested, including relatives of the wives of the two (or more?) possible grandfathers. Keep digging!

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    • #3
      Basically what John indicated. But to put it more bluntly: "Diagnosing at 3rd Cousin" when the sisters(and prospective "not sister") have samples to compare against one another is folly at best.

      Contact the sisters and see how they relate to each other on autosomal, rather than draw conclusions based on how they match with you on autosomal. While the theory is "potentially valid" it also is entirely possible that "DNA Inheritance is random" and random IS random. Sometimes you get "heads" three times, and a lone "tails" in a series of 4 coin tosses.

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      • #4
        Thanks for the comments. None further are needed. I will be contacting these dna matches to request their mutual cM matches and to other identified matches in the tree.

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        • #5
          If you are able to get all of the kit uploaded to GEDmatch, you can use the tools there to explore the situation in greater detail. Or at least, all the kits in one place, and cooperation from those involved so you can get the total shared cM and the matching segments for EVERY combination of those kits. Good luck!

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