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From: "Alastair Greenshields" <>
Subject: [DNA] Methods of comparing different genealogy DNA tests
Date: Sun, 2 May 2004 04:42:07 +0100


Bret wrote:
"I believe that it is reasonable expectation, that an organisation that
uses such laboratory testing, in its quality control, be able to provide

a guaranteed degree of accuracy as mentioned in my message; whether it
is a degree such as I have mentioned in my examples, or, higher or
lower degrees of accuracy, there should be a stated guarantee of
accuracy, nevertheless."



Hello Bret,

This is a couple of days late (have been busy updating Ybase) but the
accuracy of the lab and the accuracy of comparing two people with the
results are different.

It is a bit like perfectly reading all of the characters in a text book,
but having trouble interpreting them because the text is in a foreign
language. The reading of the DNA is excellent, it is deciding if and
when two people share a genetic link that hard figures cannot be placed
upon.

The Y-chromosome test is different from the usual forensic profile that
the FBI/police would measure. The forensic profile tests several
chromosomes that an individual will have received from his/her parents.
Each forensic marker is really two, half of each marker is from each
parent and which markers are received is a random process - meaning
siblings have different genetic profiles. This process is well
understood and the calulations fairly straightforward - and giving far
higher confidence levels (e.g 99.9999% etc.) than a Y-chromosome test
could.

The Y-chromosome in contrast is passed down virtually unchanged from
father to son. Sometimes it mutates, usually it doesn't. The rate at
which it mutates is under question and the mutation rate will likely
differ between genetic lineages. It is these uncertainties that mean we
can't pin down percentages of accuracy to Y-chromosome comparisons in
the same way that you can with a regular forensic profile. This isn't a
failure of the testing process, it's just that many factors are involved
which make the interpretation fuzzier.


Choosing the markers.


Kind Regards,
Alastair



Alastair Greenshields
Principal
DNA Heritage
http://www.dnaheritage.com

Have you searched Ybase yet? http://www.ybase.org



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