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Thread: Ancestry should show or allowing downloading of all 40 runs of ancestry analysis

  1. #1
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    Ancestry should show or allowing downloading of all 40 runs of ancestry analysis

    Ancestry says that the way each person's ancestry calculation is done, is that they perform 40 separate runs of their test algorithm on that person's DNA. Each time, a somewhat different division of the person's genome into blocks is performed.

    Each ancestry "score" represents the average score across the 40 runs, calculated separately for each ancestry.

    One problem I have with this is that no ancestry is ever determined independently of the others. As the percentage of one ancestry goes up, the percentage of some other ancestry or ancestries must go down.

    And with smaller ancestries, in particular, some divisions of the genome will effectively eliminate any actual segments, since those that exist will be small. They would be more likely to be detected -- and called -- if they're not combined with a large amount of some other ancestry. So my preferred method would involve not random division into different blocks of various sizes, but a more uniform division into small blocks.

    However, failing this it might be useful to see just what ancestries go up, or down, simultaneously with other ancestries going down, or up. It might be that my "Native American" (score of 1%, but range of 0-2%) doesn't simply move in lock-step with, say, my Great Britain or West Europe score. Maybe it moves more in relation to my "Finland/Northwest Russia" score, which is less than 1%, though the range is 0-3%.

    Or maybe the NA score moves more in relation to my "Asia Central" score (1%, range 0-3%), or my "Asian South" score (less than 1%, but same range as for "Asia Central").

    The bottom line is, Ancestry's software is going to produce some sort of call for each of the "blocks" in each of the 40 runs. Blocks which are only slightly different might not produce calls which are totally different -- at least in all cases -- but the call which seems closest for the slightly reconfigured blocks.

    This is why I prefer 23andMe's presentation of the results, regardless of whether they're actually better. 23andMe shows the location of each segment it has assigned to some ancestry. Although I'd prefer if they gave a start and end point for each segment -- as they do for matching to relatives -- at least this approach allows for direct comparison among family members.

    For example, I have a 3rd cousin who shares 5 segments with me at 23andMe. I know he's a 3rd cousin not because it's what 23andMe estimates, but because we actually do descend from the same pair of 2nd great grandparents. In fact, we descend from them on both his father's and mother's side. They're 2nd cousins, and my match and I are 3rd cousins once removed as well as 3rd cousins.

    Anyway, because of 23andMe's presentation of its ancestry predictions, I can see that one of the segments we share is a location called as "Native American" for both of us. And, it happens that we both have confirmed Native American ancestry through one of those common 2nd great grandparents.

    My 3rd cousin's Native American ancestry is given as 4.1% in Ancestry Composition, while mine is only 2.0%. But remember that he is descended from the known NA ancestry through both parents. My descent is only through my mother.

    I actually have other examples I can point to, but the point is that all we'd be able to compare in Ancestry would be the percentages. We'd have no idea whether the same side was actually involved -- or whether it perhaps involves an entirely different set of ancestors for each of us.

    Of course, I've gotten a bit off my main point, which is that knowing how the different ancestries move in relation to each other across the 40 runs could be useful information. (Though, again, a completely different approach involving both a chromosome browser and predicting ancestry by segments would be even better.) If Ancestry doesn't want to display anything like this, believing it too complicated, they could at least make it available as a download.
    Besides British-German-Catalan, ancestry includes smaller amounts of French, Irish, Swiss, Choctaw & another NA tribe, possibly Catawba. Avatar picture is: my father, his father, & his father's father; baby is my eldest brother.

    GB

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  3. #2
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    I wish I'd written "Show or Allow" in the title instead of "Show or Allowing", which is just a typo. But as far as I can tell, there's no way to edit a thread title.
    Besides British-German-Catalan, ancestry includes smaller amounts of French, Irish, Swiss, Choctaw & another NA tribe, possibly Catawba. Avatar picture is: my father, his father, & his father's father; baby is my eldest brother.

    GB

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    Has Ancestry ever said why they don't want to add a chromosome browser?

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    "Privacy issues".

    Basically, the idea is that you reveal what SNPs are on the shared segments when you give the exact locations of the shared segments. This is of course true, but presumably they'd provide an "opt in" or "opt out", and the only people who would be sharing would be people who have a shared DNA segment or segments.

    23andMe, MyHeritage, and FTDNA have all found ways to provide a chromosome browser and to also respect individual privacy -- and in any case, you don't have to test -- so I don't see why Ancestry can't.

    As it is, if you're on Ancestry and want to look at your shared segments, you pretty much have no choice but to upload to either GEDmatch or perhaps FTDNA.
    Last edited by geebee; 08-07-2018 at 04:23 AM.
    Besides British-German-Catalan, ancestry includes smaller amounts of French, Irish, Swiss, Choctaw & another NA tribe, possibly Catawba. Avatar picture is: my father, his father, & his father's father; baby is my eldest brother.

    GB

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    Folks might be interested in this piece from "The Ancestry Insider": http://www.ancestryinsider.org/2017/...let-up-at.html
    Besides British-German-Catalan, ancestry includes smaller amounts of French, Irish, Swiss, Choctaw & another NA tribe, possibly Catawba. Avatar picture is: my father, his father, & his father's father; baby is my eldest brother.

    GB

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     Saetro (08-16-2018)

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    Quote Originally Posted by geebee View Post
    Folks might be interested in this piece from "The Ancestry Insider": http://www.ancestryinsider.org/2017/...let-up-at.html
    If MyHeritage continues its rapid growth, especially within existing Ancestry markets, I predict that this privacy concern will disappear.
    One way or another.

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