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Scale of Time and Space in Admixture
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Screenshot 2016-09-30 08.23.21 As you may know in Britain there is a new direct to consumer genetic testing service, Living DNA. Debbie Kennett has a post up where she talks about how it works and why it’s different. For now it is British focused, and leverages haplotype-based methods with the PoBI database to give really fine-grained analysis to their customers on those sceptered isles.

Brought to you by the same people who brought you FineStructure, this is a major offering in this space.

But there’s a more general issue I want to comment on. In the video accompanying the website, one of the presenters states that people are “very surprised how admixed” humans are. This depends on scale.

Let’s start at a time, 0. In the short term you are not very admixed usually. Outside of the Americans and other settler societies admixture is not common on the scale of recent generations. But as you go further back, you become quite admixed. E.g., The Geography of Recent Genetic Ancestry across Europe showed lots of admixture on 1,000 year scales within Europe. David Reich’s lab has shown lots of admixture between very diverged populations on a 5,000 year scale. But as you go further back the ‘admixture’ gets lower and lower, and at some point you hit the species barrier, and you see the same genealogies coalescing again and again through the bottleneck.

Now, look at space. As distance is ~0 you’ll see lots of admixture. But as you push further and further away, the admixture drops. At some point the admixture is quite boring. Ergo, all the “you are 100% European” results from DTC companies.

The two dimensions look quite different. Admixture increases as you go further back in time…until it doesn’t. You’re hitting the “species” taxonomical barrier. In terms of space, admixture decreases the further you go away from your focal point of interest.

 
• Category: Science • Tags: Genetics 
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  1. Rick says:

    Admixture occurs when two or more previously isolated populations begin interbreeding.

    So any argument will mostly be dealing with whether or not a population was ‘isolated’ before the interbreeding.

    And this is just a matter of time. If you go back far enough… you already know… whatever.

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  2. Alan says:

    Of course the presenter will say that people are surprised at how admixed they are. They’re trying to sell their product and they want people to be intrigued enough to buy it. It’d be poor marketing to say, “your results will show that your ancestry is exactly what you think – 100% British.”

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    • Replies: @Sean
    "Fine grained" results will show more non British Isles ancestry than you think, because I stumbled on an idiot's guide to the implications, and the paper Razib links to in the post shows (if I understood the guide) that everyone in the UK is related to all Europeans of a millennium ago, but that does not mean everyone has genes from each of them (even if you have genes in common with them) because your lines of ancestry converge to make you a multiple descendant of an individual ancestor, giving you DNA from fewer ancestors than the (theoretical) living individual who has totally-unrelated-to-each-other ancestors all the way back.

    My impression is that people in the field, even those in a testing business, don't push anything but medical research into diseases, and maybe proof of admixture across national boundaries.

    http://www.huffingtonpost.com/2015/07/14/kuwait-mandatory-dna_n_7795442.html


    Kuwait ... the first nation to force all residents and visitors to hand over DNA, risking its reputation and more, warns geneticist Olaf Rieß, ESHG President.
     
    German geneticists are the masters now.
  3. ohwilleke says: • Website

    “As distance is ~0 you’ll see lots of admixture.”

    We would hope that the asymptote is a bit more than zero. Maybe a peak at 100 meters for the girl next door? Otherwise you’d be having kids with your siblings and parents. ;)

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  4. Sean says:

    [i deleted the content here because you posted a link to an article ABOUT the paper that i actually posted the link to. that is what i call 'not value-added'. i don't post paper links for no reason. -razib]

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    • Replies: @Sean

    But as you go further back, you become quite admixed. E.g., The Geography of Recent Genetic Ancestry across Europe showed lots of admixture on 1,000 year scales within Europe
     
    I, for one, didn't follow what you meant by that.
  5. Sean says:
    @Sean
    [i deleted the content here because you posted a link to an article ABOUT the paper that i actually posted the link to. that is what i call 'not value-added'. i don't post paper links for no reason. -razib]

    But as you go further back, you become quite admixed. E.g., The Geography of Recent Genetic Ancestry across Europe showed lots of admixture on 1,000 year scales within Europe

    I, for one, didn’t follow what you meant by that.

    Read More
  6. “Mixed race” is a pretty relative term. Just breed for the phenotype you want, really.

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  7. Sean says:
    @Alan
    Of course the presenter will say that people are surprised at how admixed they are. They're trying to sell their product and they want people to be intrigued enough to buy it. It'd be poor marketing to say, "your results will show that your ancestry is exactly what you think - 100% British."

    “Fine grained” results will show more non British Isles ancestry than you think, because I stumbled on an idiot’s guide to the implications, and the paper Razib links to in the post shows (if I understood the guide) that everyone in the UK is related to all Europeans of a millennium ago, but that does not mean everyone has genes from each of them (even if you have genes in common with them) because your lines of ancestry converge to make you a multiple descendant of an individual ancestor, giving you DNA from fewer ancestors than the (theoretical) living individual who has totally-unrelated-to-each-other ancestors all the way back.

    My impression is that people in the field, even those in a testing business, don’t push anything but medical research into diseases, and maybe proof of admixture across national boundaries.

    http://www.huffingtonpost.com/2015/07/14/kuwait-mandatory-dna_n_7795442.html

    Kuwait … the first nation to force all residents and visitors to hand over DNA, risking its reputation and more, warns geneticist Olaf Rieß, ESHG President.

    German geneticists are the masters now.

    Read More

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