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Thread: How Far Back Does A Current Autosomal Karyotype Go?

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  1. #1
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    How Far Back Does A Current Autosomal Karyotype Go?

    If I'm a man with one sub-Saharan African (sSA) ancestor from 500 years ago, and it's my mother's mother's mother.... etc., my mitochondrial DNA will tell me that. But if every other ancestor was European (including my paternal ancestry) my Y chromosome and autosomals will tell me that.

    But will my remote, fractional sSA ancestry show up on my autosomal karyotype? In other words, what really does my current autosomal karyotype reflect?

    (In case you're wondering, this is a made-up scenario.)

  2. #2
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    It depends on the test.

    Many open source calcs (eg. the GEDmatch ones) will show extremely distant ancestry. I'm mtDNA haplogroup H1, which originated in East Africa over 30,000 years ago. Yet on GEDmatch I sometimes score trace amounts of SSA, usually East African. I have no known African ancestry beyond this. So an SSA ancestor from 500 years ago would likely show up in your karyotype.

    Commercial services like 23andme, Ancestry etc. generally only go back a certain amount of time or exclude trace amounts from their estimates. However, it is still common for trace amounts to show up.
    Target: mildlycurly_scaled
    Distance: 1.3578% / 0.01357814
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  3. #3
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    Quote Originally Posted by mildlycurly View Post
    I'm mtDNA haplogroup H1, which originated in East Africa over 30,000 years ago.
    First time I hear that. The haplogroup originated in Near East or Caucasus:
    https://academic.oup.com/mbe/article/24/2/436/1148196

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  5. #4
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    No it nearly impossible.
    If you just got one sub-Saharan ancestor 500 years ago, It'ts about 20 generations back. Remember that your great-grandfather for example only give you about 12.5% of your admixture, and his father only 6,25 % and so on. It would disappear fast.
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    51.6 VK2020_IRL_Eyrephort_VA = Germanic
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  6. #5
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    500 years ago, thats about 18 generations, so then you have on paper maybe up to 100 thousand ancestors. Many of them will not be present in your genome; if you go back 7 generations, it is likely that you have DNA from almost all your ancestors, but if you go back further, many ancestors will "drop out" every generation. Your mother might have a small segment from a particular ancestor 10 generations ago, but if she did not transmit that segment to you, he has dropped out.

    It is possible in some cases to attribute certain DNA-segments to ancestors from 10-14 generations back (say 1600s), but if you go further back, the segments are so small that it becomes difficult to distinguish between identical-by-descent and identical-by-chance segments.
    In the case that you indeed inherited autosomal DNA from that subsaharan ancestor from 18 generations ago, the question is whether it can be recognized as such; perhaps you get 0.1% Sub-Saharan in a test, but such a small percentage might also be noise. Besides that, it may also be from a different yet unknown subsaharan ancestor - if you go back 18 generations, how much of your pedigree do you really know? The chance is large that more than 90% is unknown.

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