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Archiver > GENEALOGY-DNA > 2010-05 > 1274922659


From: (John Chandler)
Subject: Re: [DNA] Does Sardinia hold the key to the debateabout Neolithicor Paleolithic dispersal of R-M269?
Date: Wed, 26 May 2010 21:10:59 -0400
References: <AANLkTinEq_2xAofI_ttFnOgfhjWcPIrOmfH58K4TGdRa@mail.gmail.com><REME20100526163921@alum.mit.edu><C34F1DD2221241CFA5D1ACB29B43D847@john>
In-Reply-To: <C34F1DD2221241CFA5D1ACB29B43D847@john> (ajmarsh@arrrg.org)


John wrote:
> There are ways of minimizing contamination. For example, I believe many
> labs testing Y-DNA use only female staff, so that they can't contaminate
> samples with their own Y-DNA.

Ah, but these are labs that test ... other Y-DNA, and almost certainly
a large part of the testing is done on R1b samples.

> If there was an important isolated site being excavated, and it was hoped to
> obtain good archeological Y-DNA tor testing, the whole project could be
> carried out to the highest standards. Female archaeologists only, female
> lab staff only, a new lab and new equipment to avoid risks of contamination.

Frankly, I don't see Y-DNA tests rating high on the priority list of
archeologists.

> If you feel that contamination is such a rampant problem, and the scientific
> community so unreliable that they can't sterilize equipment, identify and
> account for contamination, then I suppose every person in prison convicted
> on DNA evidence will be quoting you in an effort to get their "beyond
> reasonable doubt" conviction overturned.

You have missed an important point. The problem with ancient DNA is
that there is often nothing left to recover at all. This is vastly
different from testing fresh (and, by the way, autosomal) DNA samples
from crime scenes. For aDNA analysis, valiant efforts are made to
AMPLIFY even the tiniest trace of DNA. It is not hard to eliminate
the signals from mildew and insects, but the screening process has to
go case by case. Even one sample that slips through is a catastrophe
if the intention is to detect "modernesque" DNA from antiquity.

> Are you placing into question King Tut's results which appear as though they
> might be R1b?

I haven't heard anything to convince me that those were really King
Tut's results anyhow.

> I have heard there are various means to identify and allow for possible
> modern contamination, and over time, statistical analysis of multiple
> results, and independent testing at different labs, would enable the chances
> of contamination to be reasonably accurately evaluated.

It depends in part on how much testing is done on the samples.
Certainly, intralab contamination can be ruled out by going to several
labs and testing enough loci. However, in situ contamination by, say,
a 3rd-century hermit would be extremely difficult to detect. Don't
forget we're talking about Europe here.

John Chandler


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