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When do you have enough data to attach an parent to a child?

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  • When do you have enough data to attach an parent to a child?

    When does one have enough data to assign parentage to a child?
    Not sure the best way to lay this out, but here’s what I have.
    My three aunts have tested on’s older test which was then uploaded to FTDNA years ago. Born between 1924 and 1941, their grandmother Mary was born out of wedlock in 1841 in England. (Mary’s son, the father of the three aunts, was in his 40s when he married).
    Mary came to the US as a 12-year-old in 1853 with her grandmother. Never returned to England. Died in 1916.
    The three aunts pull in DNA matches that are in the 2nd-4th cousin ranges with a number of people for whom I cannot find any connection, but whom are all descended from a Gibson and Peggy. Some of these matches are:
    --4th great granddaughter matches two aunts (18.6 cm/ 2 segments and 11.7 cm/ 1 segment). Descends from their son Joseph
    --2nd great grandson, from England, matches all three aunts (100.5cm/4 segments, 32.6cm/2segments, 30.3cm, 2 segments). This match has a son who tested and he matches the tree as well (52.7cm/2 segments, 17.7cm/1 segment, 17.8cm/1 segment). The latter match would be a 3rd great grandson. Descends from Gibson and Peggy’s son George (too young to have been the father of the grandmother Mary Robson.
    --And then there is this match from a different brother Gibson who married later in life. This match, an 80-year-old woman from England, would be a 3rd great granddaughter of Gibson and Peggy. She matches all three aunts, and 5 descendants of deceased sisters of the 3 aunts.
    Aunts: 207cm/7 segments, 195.6 cm/10 segments, 60.2cm/4 segments. Nephews and niece of 3 aunts: 113.9cm/4 segments, 104.8cm/5 segments, 50.5cm/segments, 39.2cm/2 segments (4 nephews who are all brothers), and finally the niece 51.5c,/2 segments.
    This 80-year-old woman had tested on on their newer chip and she kindly tested on FTDNA for me, as did her granddaughter. (She is listed before any 2nd cousins, 1R, following two 1st cousins, 1R. in her matches with my Aunts…so there is this lone unknown relation in a sea of known cousins descended from English families who also came over in the 1840s/1850s.)
    FTDNA Matches with aunts and nephews.
    229 cm/longest block 112, 218cm/112 longest block, 78cm/longest block 23 cm. Nephews: 142cm/41 longest block, 127cm/33 longest block, 90cm/27 longest block, 61cm/22 longest block.
    Peggy and Gibson’s farm was about 1500 feet from where Mary’s family lived in the 1841 census.
    If I link Gibson to Mary as “father,” most of my unknown matches make sense through Gibson and Peggy’s ancestral lines. But I would hate to be wrong and put it out as fact…

  • #2
    Dear MJW,
    It appears to me that these DNA results would qualify as a "Triangulated match" that points back to Gibson and Peggy as the parents IMHO.
    Rory Bowers
    Co- Administrator, Bowers DNA Project


    • #3
      Hi MJW ... there's an online tool "What are the Odds?" (WATO) that can help you. It's part of the dnapainter site, and so you may have to register with dnapainter to use it.

      It requires matches of 40cm or more (that's the total cM shared with a match, not individual segments). You use the tool to create a pedigree tree with the known common ancestors at left, and the "target" (one of the aunts who's tested) at right; then you place the known matches in the tree, in their correct locations, and add hypotheses about the relationships to your "target". The tool rates relative (no pun) probabilities, so the more hypotheses the better. There are instructions (read the FAQ) on the site, and there's also a user/support group on facebook. Note: if there's a possibility one of Gibson and Peggy's sons was the father, the tool won't be able to distinguish between them unless you have matches descended from all of them.

      WATO is here:
      Last edited by Fern; 7 December 2019, 04:49 PM.