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Thread: Question about ancient DNA and autosomal tests

  1. #1
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    Question about ancient DNA and autosomal tests

    Hello,

    I have a question: If you only inherit DNA from up to 5 generations then how can autosomal ethnicity tests tell you your ancient DNA? Is it because any population will have markers 'stored' in their DNA chromosones from previous populations?

    Furthermore, i've read a bit about how a persons DNA is looked at for having certain similarities to reference populations. But how can old bones say of Loschbour etc... translate into data that can be compared with my DNA sample?

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    Here's my understanding.

    Every piece of your DNA you inherited from every generation going all the way back (except for the mutations which are yours) but after a handful of generations you don't necessarily have any DNA from every ancestor at that level. And then each generation going further back the percent of ancestors that actually passed DNA gets down to you gets smaller, but it will never reach zero because your DNA has to come from somewhere.

    DNA gets mixed every generation so pieces from a specific ancestor get smaller and smaller but at some point you're more likely to lose the entire segment then to have that segment broken into still a smaller piece. So if there's a 1 cM piece of DNA that is common in a population each generation that occurs 99% of the carriers will pass it along whole and only 1% will break the piece up for their children. For the 99% half will lose the segment and the other half will pass the whole thing along. And if it's common the children that had a parent that did not pass that piece of DNA may have gotten it from the other parent. And if the piece was split by one parent the other parent may have the other part of that piece of the segment meaning the descendant might not even notice that their segment was broken and reformed.
    Daughter's ggg grandparents(father to left, mother to right)
    Male: R-BY4242, R-Z344, ?, ?, E-V13, ?, E-L29, ?, R-Z20907, ?, ?, ?, R-L2, R-L20, ?, ?
    Female: ?, ?, ?, ?, ?, ?, ?, W6a, ?, N1b1, ?, B4a1a1, ?, ?, ?, H3h, ?, ?, ?, ?, ?, ?, ?, I3a, ?, ?, ?, ?, ?, ?, ?, K1c1g

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    Quote Originally Posted by Hobknobbob12 View Post
    Hello,

    I have a question: If you only inherit DNA from up to 5 generations then how can autosomal ethnicity tests tell you your ancient DNA? Is it because any population will have markers 'stored' in their DNA chromosones from previous populations?

    Furthermore, i've read a bit about how a persons DNA is looked at for having certain similarities to reference populations. But how can old bones say of Loschbour etc... translate into data that can be compared with my DNA sample?

    Coincidentally, our colleague Finn just posted an article that touches on this, written by Roberta Estes.


    Autosomal DNA, Ancient Ancestors, Ethnicity and the Dandelion

    https://dna-explained.com/2013/08/05...the-dandelion/
    Known Paper Trail: 45.3% English, 29.7% Scottish, 12.5% Irish, 6.25% German & 6.25% Italian. Or: 87.5% British Isles, 6.25% German & 6.25% Italian.
    LivingDNA: 88.1% British Isles (59.7% English, 27% Scottish & 1.3% Irish), 5.9% Europe South (Aegian 3.4%, Tuscany 1.3%, Sardinia 1.1%), 4.4% Europe NW (Scandinavia) & 1.6% Europe East, (Mordovia).
    FT Big Y: I1-Z140 branch I-F2642 >Y1966 >Y3649 >A13241 >Y3647 >A13248 (circa 930 AD) >A13242/YSEQ (circa 1075 AD) >A13243/YSEQ (circa 1660 AD).

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    Actually, we do not know the composition of the 50/50 from your parents. We do not know if entire intact segments are passed on or not. It is certainly not a random process of DNA dilution/mixing through generations. If so, we would be 100% sure no intact segments from say, bronze age ancestors, would be present in our genes. A proof of that is shared segments you have with other individuals in other parts of the world, which are often related to specific ethnic background. For instance, I have a defined segment on my chromo 9 which is always matching swedes. I have no scandinavian ancestry besides my genealogical Norman roots going back more than 1000 years ago. If random dilution was at play, none of those segments would have remained intact.

    Tree collapse is at play as well as families historically intermarried within their kins and alliances. So, the perfect theoretical family tree doesn't exist (and therefore perfect mathematical dilution). there are lots of duplication in ancestors and obvious reinforcing effects on some DNA segments.

    Just my two cents. Would like to hear more views on the topic.
    Last edited by Theconqueror; 03-08-2019 at 04:17 PM.
    K8: French East/German South/Austrian 26%, French North East/Belgian/German West 25%, French North 25%, Irish/Scottish/Welsh 10%, French South/French Basque 9%, German East/Czech/Austrian 5%
    K16: German/Czech/Austrian 33%, French/Belgian 23%, Portuguese/Spanish 22%, Irish/Scottish/Welsh 13%
    K36: German Rheinland-Pfalz 35%, French North West 27%, Spain 27%, Ireland 11%
    G25: German 40%, French 28%, Spanish 23%, Irish 9%
    K16: German 50%, French 19%, French East 9%, Spanish 8%

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    You also share large pieces of DNA with ancestors further back than 5 generations. However, the further you go back, the smaller the segments become and some ancestors will not have contributed to your DNA because of the "recombination lottery" every generation.
    See also this article, which has nice graphs IMO.

    As for the affinity with ancient DNA: imagine some tomatoes and a blender. After a few seconds of mixing, you might still recognize the tomatoes, but after mixing for a while, you get an undefined red mass, but it still tastes like tomatoes.
    Last edited by Pylsteen; 03-08-2019 at 04:57 PM.

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    Quote Originally Posted by Pylsteen View Post
    You also share large pieces of DNA with ancestors further back than 5 generations. However, the further you go back, the smaller the segments become and some ancestors will not have contributed to your DNA because of the "recombination lottery" every generation.
    See also this article, which has nice graphs IMO.

    As for the affinity with ancient DNA: imagine some tomatoes and a blender. After a few seconds of mixing, you might still recognize the tomatoes, but after mixing for a while, you get an undefined red mass, but it still tastes like tomatoes.
    Really informative thanks!

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    Quote Originally Posted by Theconqueror View Post
    Actually, we do not know the composition of the 50/50 from your parents. We do not know if entire intact segments are passed on or not. It is certainly not a random process of DNA dilution/mixing through generations. If so, we would be 100% sure no intact segments from say, bronze age ancestors, would be present in our genes. A proof of that is shared segments you have with other individuals in other parts of the world, which are often related to specific ethnic background. For instance, I have a defined segment on my chromo 9 which is always matching swedes. I have no scandinavian ancestry besides my genealogical Norman roots going back more than 1000 years ago. If random dilution was at play, none of those segments would have remained intact.

    Tree collapse is at play as well as families historically intermarried within their kins and alliances. So, the perfect theoretical family tree doesn't exist (and therefore perfect mathematical dilution). there are lots of duplication in ancestors and obvious reinforcing effects on some DNA segments.

    Just my two cents. Would like to hear more views on the topic.
    From a genetic point of view, although the SNPs that are evaluated for these tests are supposed to be neutral, there is a selection going on for certain advantageous genes or against detrimental genes. Now if some SNPs are located close to these gene regions that are positively selected, they will be kept as a side effect of that selection. Moreover, regions that are close to centromers (middle of the chromosomes) recombine less etc etc. We don't know enough about the genome organisation to understand such mechanisms.

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    Thanks for the link to those articles, interesting reading. Still don't really get how we can compare ancient DNA to living samples. I understand, reading the very interesting eurogenes blog which I've started to do more now, that populations through out history are basically just a clustering of indviduals over time. And there are distinct patterns in the dna of these populations within these clusters that allow them to be differentiated from other populations. This article is a good example https://www.nature.com/articles/s41467-018-08220-8. Don't understand the DNA bit, but what it can tell us about migration patterns, the archeological stuff etc.. is pretty cool.

    So even if my autosomal dna only goes back 5 generations, the dna of the modern populations now surely show a distinct pattern in their dna in comparison to other populations. For example, the celts, anglos, britonic celts, viking, normans all formed distinctive patterns within their DNA and formed the patterns of the modern population of UK? But how long does it take for distinctive patterns to emerge and how long for them to change?

    Are these differences based around mutations which are related to climate?

    Forget trying to understand how they can extract the actual dna from old graves, but once they have it.... they now have a library of data which they can refer to. So a population that has a series of TT AG or whatever in segments of DNA will be placed on PCA and positioned relative to all the other samples.

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