GENEALOGY-DNA-L Archives

Archiver > GENEALOGY-DNA > 2002-04 > 1017879480


From: "John F. Chandler" <>
Subject: Re: [DNA] BROOKING network diagram
Date: Wed, 3 Apr 2002 19:18 EST
In-Reply-To: OrinWells@wells.org message <4.1.20020403070620.0477f9c0@wells.org> of Wed, 3 Apr 2002 08:27:02 -0700


The burning question:
>I have seen this page - but what does 'M' really mean ?
>http://members.attcanada.ca/~bgh/genetics.html

We must remember that these tests are conducted in batches. In other
words, the test DNA is "incubated" with a combination of PCR primers
for several different loci at once. The primers are supposed to work
in pairs by binding one to each end of each marker and thereby selecting
the markers out of the entire genome. By design, the primers are
supposed to bind only at the one spot each, but some people presumably
have mutations elsewhere such that some primers can bind at an extra
spot. If the extra binding spots result in selecting segments of DNA
that are vastly different in length from the expected markers, then
there is no problem, but bad luck could result in extra segments that
are confused with the markers being measured. That would mean "multiple
peaks" with no clear idea of which peak is the intended marker and which
is the phony. If this is the source of the problem, then the multiple
peaks will indeed be repeatable every time, UNLESS the lab gives up
the multiplexing scheme and does the confusing marker by itself in a
separate run. I don't know whether this is the mechanism for DYS425,
but it's conceivable.

John Chandler

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