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Auditing my Family Tree using DNA matches

Discussion in 'DNA Questions and Answers' started by Derek Baker, Jun 29, 2020.

  1. Derek Baker

    Derek Baker LostCousins Star

    I have recently started auditing my tree using Ancestry DNA matches.
    I have two main objectives for doing this.
    1. Confirm that my family tree researched over the last 30 years is accurate. (Have I made the right choice when no clear evidence existed to enable me to decide if my ancestor was one of a number of possibilities?)
    2. See if any ancestors were playing away from home! (If Great Great Granddad was not in fact Great Great Granddad who was the real one (I suppose I will never know but DNA may give some clues).
    I wonder how many trees have cuckoos in the nest. Happens in the best of families!)

    To start with I chose my Paternal Grandmother's line because a. it is a more unusual surname and b. there is a big brick wall there due to missing Methodist chapel records from before 1800, I am hoping to find DNA matches to the surname in the 5th to 8th cousins which would give a clue s to who my 5G Grandfather was.
    I then went back 5 generations on the tree (born ca 1800) and entered into the Ancestry DNA matches 'surname in matchs' trees' search box, one by one as many different surnames that I know of in that branch. So all results would be for genetic matches to myself.
    The search results were few (never more than 10 per surname) and fairly inconclusive most had no common ancestor.
    A few had a common ancestor and I was able to match that to my tree making our common female ancestor a genetic link. This is better if more than one genetic match all link back to the same common ancestor. It legitimises all male and female ancestors on the direct line between the two of us. I think!
    A few of those that did not have a common ancestor had done enough research for me to be able to identify their line in the tree and thus establish a common ancestor.
    Sadly the majority just seem to have just taken a DNA test and identified a couple of generations. In these cases it is impossible with any degree of confidence to establish how they are related.
    However I did find 10 people (Cousins) who are related via various branches of Gran's tree. So looks like her ancestors are the right ones back to 1800. I must now go back a few more generations.

    Having done this for all actual DNA matches in my Paternal Grandmothers line I turned to doing Ancestry Family Tree searches to see if I could shake out a few cuckoos.
    I entered the forename, surname and date of birth for my G G Grandfathers, in the line I was checking, one by one into a general Ancestry search, selected Collection Focus - England and unchecked all boxes except family trees. This gave a lot of results, hundreds, I started looking at the trees for those with the most similar looking names and dates and place of birth to names in my tree.
    I ignored any who had already shown up as DNA matches as that would be just duplicating what I had already done previously.
    Sadly using this method I found no additional cousins and failed to shake out any cuckoos.
    On checking the tree owners of all the trees I had looked all just said that 'XXX is either not a DNA match or has not taken a DNA test'. I do wish they would be more explicit. Knowing if the tree owner had taken a test and was NOT a match would be useful, it would indicate that one of us has a 'wonky' tree.
    Knowing that someone whose tree showed them being descended from my GGG grandfather's brother and was NOT a genetic match to me would likewise be useful knowledge. Again it may show up an inaccurate tree or something else?

    Sorry about this being a little long but had to try and explain it all.
    Has anyone tried this? Are my assumptions correct?
    Any positive help welcome.
  2. Helen7

    Helen7 LostCousins Superstar

    Don't forget that DNA matches are not guaranteed beyond 2nd cousins, and the chances go down rapidly beyond 4th cousins. Someone descended from your GGG grandfather's brother would (assuming same generation as you) be your 5th cousin, and it would be more likely for them NOT to have a DNA match with you - about a 32% chance of a match according to the table in Peter's Masterclass.
  3. Derek Baker

    Derek Baker LostCousins Star

    I am not looking to add names to my tree using individual DNA matches.
    All the names I am checking (Auditing) are already in my tree, some with a great degree of confidence others less so.
    The point of doing the Audit is to find confirmation or otherwise via DNA match or non match.
    I am collecting a body of evidence to prove or disprove the correctness of my tree.
    If one DNA match has independently arrived at the same ancestor as I did then that is some positive evidence, if a number of others from different branches have also arrived at the same conclusion then the correctness of the original research is statistically improved.
    Similarly if a significant number of people have arrived at the same ancestor but are NOT DNA matches then that would count against the correctness of the original research.
    It is preciously this in your highlighted quote that I am unable to determine because of the way Ancestry phrase their relationship to me of the tree owner.
    Meaning that at present I am unable to determine the status of non DNA matches who seem to have the same name in their tree.
    Rest assured that I do NOT add people to my tree without thorough investigation. I never trust other peoples research.
  4. Helen7

    Helen7 LostCousins Superstar

    I wasn't for one moment suggesting you were. It was just that you seemed to imply that finding a documented cousin who is not a DNA match means there is something wrong with your or their research, which is not necessarily the case due to the 'pot-luck' nature of DNA matches between distant cousins. Also, you and the other person could have a DNA match and be related, but have made the same mistake in tracing your common ancestry.

    However, I do take your point about a body of evidence. Significant numbers one way or the other could tend to point to the correctness or otherwise of the research, though you'd need to be careful about drawing such conclusions on limited numbers. And yes, to that end I can see how it would be useful to know if 'non-matches' had tested or not.
  5. peter

    peter Administrator Staff Member

    That's why DNA only confirms the research as far back as the common ancestor(s). To get back further you need a match with a more distant cousin who shares a more distant common ancestor.
    • Agree Agree x 1

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