Wednesday, April 04, 2018

Comment: Re: confused

Looks like my IntenseDebate comments system is hosed. At least it doesn't work consistently.

So, to reply to a comment until I figure out how to make things work:

Suppose you said that X and Y had a similar ancestry profile of a Norwegian and Italian mix, except that Y also had 22% Japanese ancestry. It makes one wonder, what does a "similar ancestry profile" mean?

How about "X is half tin and half copper" vs. "Y consists of equal parts of tin and copper with 22% arsenic"? Seems like the obvious analogy to me.

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This analogy doesn't work for me for several reasons:

First of all, X and Y are different alloys, some variety of bronze versus arsenical bronze.

Next: the X itself consists of 14-42% AASI (and the rest Iranian farmer and Siberian Hunter Gatherer)

So this is like saying X is 14% tin and 86% copper or 42% tin and 58% copper and Y is various proportions of tin, copper and arsenic (arsenic averaging 22%).

Next: What does "similar ancestry profile" mean of X and Y when X and Y don't share at least 22% of their ancestors?

Next: since when is 78% of a genome similar to 100% of another? 

Next: A majority of Indians are somewhere on the ANI/ASI cline with little other admixture.  Would you say they "share the same ancestry profile"?

Next: Out of 246 groups of Indians that this pre-print had genetic profiles for, they excluded 106. Some for paucity of data; but others for having something more than just ANI/ASI.  i.e., for that part of the analysis, these 106 groups did not have "similar ancestry profiles".

Next: just as a practical thing - if someone said, I have the same ancestry profile as European Americans but also 22% African - well, unless they are "passing" this someone has gone from being white to being black.  Trump supporters (well, some of them) would likely riot over a statement that they share an ancestry profile.

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IMO, on an entirely different tack, I get a suspicion that some of the genetics people don't really understand the algorithms that underlie their computational analytic apparatus; it is largely black-boxes to them.

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 PS: Let's get to some amusing applications of "similarity".

These two geometric figures are similar though one is triangle and the other is a quadrilateral.

"I'll offer you a similar deal as I offered him, except you'll pay 22% more."

Comments (4)

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There is one more confusion , Steppe contain EHG + ATF(depicted by orange color) with some East Asian component in the later period. The aDNAs from South Asia in the paper don't seem to contain the EHG component at all but only Anatolian farmer related ancestry (Page 22 of the pre-print). So, how come it becomes Steppe ancestry ? Isn't it a twist of words when it's actually anatolian (the older Tepe_Hisar_C and Haji_Firuz_C already contain substantial ATF related ancestry ) ? Can you please clarify ?
Similar means identical in some respects but not all. Ancestry is traced by finding unique SNPs in ancestral populations and in subsequent populations. Suppose X has clusters of such SNPs from two separate ancestral populations A and B but not from C. Then we can assume X descended from both A and B but not C. If a later population Y then has such SNPs found in X and C, its reasonable to assume that Y is similar to X in that it is descended from A and B but different in that it is also descended from C.

Don't forget that such variant SNPs are rare in the genome.
1 reply · active 364 weeks ago
There needs to be a definition other than "that is what ADMIXTURE shows" (which is the answer one of the authors of the pre-print gave me when I asked what "similar ancestry profile" means. Your comment begins to give an answer.

So, the Indus_Periphery individuals (3 in number from 3100-2200 BCE) have a similar ancestry profile with the 41 individuals from Swat (1200-0 CE).

I assume Steppe_MLBA corresponds to some set of Steppe individuals whose aDNA has been found. Would it be correct to say that the 41 individuals from Swat and Steppe_MLBA have a similar ancestry profile?
23&Me says that several percent of its self-identified European Americans have some African ancestry. This can be a shock to racists, but the few people I know in that category are quite proud of it.

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