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Gedmatch Query

Discussion in 'DNA Questions and Answers' started by AlanB, Oct 5, 2020.

  1. AlanB

    AlanB Member

    I've noticed an anomaly in my Gedmatch matches recently. When I do the One To Many search it gives me the number of shared cM and an estimate of when the most recent common ancestor was, but sometimes when I do the 1 to 1 for that person the figures are different. One particular match I was interested in had 4.7 generations on One to Many but 6.4 on 1 to 1. Other matches have the two figures identical.

    I assume that Gedmatch use a different algorithm for the two types of matching, but why would they do this? And which one should I believe?
    Last edited by a moderator: Oct 6, 2020
  2. peter

    peter Administrator Staff Member

    Neither of them.
  3. AlanB

    AlanB Member

    Please explain, are you not a fan of Gedmatch?

    It's important to me that I understand this. I'm working with the shared matches of myself and my 4th cousin to try and break down a 40 year old brick wall.
  4. peter

    peter Administrator Staff Member

    The problem is that a 21cM match (which is what 4.7 generations typically represents at GEDmatch) could be anything from a 2nd cousin once removed to an 8th cousin, or even more distant. It could even be spurious if it's in a pile-up area. My advice is to stick to Ancestry - they have a far larger database and their site is generally much easier to use.

    I rarely recommend using sites other than Ancestry - it requires a level of understanding of the limitations of DNA that few people have.
  5. AlanB

    AlanB Member

    Hi Peter, thanks for the reply. It's likely I'll test with Ancestry at some point in the future, though I doubt I can persuade my 4th cousin to pay again! We both tested with FamilyTreeDNA and I've uploaded our DNA to Gedmatch and Myheritage.

    Incidentally I have a genetics degree (it was over 40 years ago however) so I think I understand DNA a bit more than most people, always willing to learn more though.
  6. peter

    peter Administrator Staff Member

    Understanding genetics will certainly help you to understand the limitations inherent in genetic genealogy when you learn about them (although a statistics degree would probably be more helpful).

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