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Archiver > GENEALOGY-DNA > 2002-11 > 1036183680


From: "John F. Chandler" <>
Subject: Re: [DNA] Forensic Markers
Date: Fri, 1 Nov 2002 15:48 EST
In-Reply-To: Nicholas.Penington@downstate.edu message <OF1FC6AA7C.1770649F-ON85256C64.006EB989@downstate.edu> of Fri, 1 Nov 2002 13:22:28 -0700


Nick wrote:
> What if the crime took place in a part of the
> country from where Mr. Blackett's ancestors originated and multiplied for
> many generations!

The CODIS tests are for autosomal markers, which get reshuffled from
generation to generation. None of Blackett's loci had a frequency
below 1%, so the rareness of his overall pattern doesn't depend on
any one specifically rare allele. Note, in particular, that the
expected number of matches to any given pattern is the product of
the pattern's frequency within the relevant population pool and the
size of that pool, summed over the whole world. Even if a particular
allele is especially common in some village or other, there are too
few people there to change the overall likelihood of a match.

John Chandler

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