GENEALOGY-DNA-L Archives

Archiver > GENEALOGY-DNA > 2007-02 > 1171598609


From: (John Chandler)
Subject: Re: [DNA] TMRCA
Date: Thu, 15 Feb 2007 23:03:29 -0500 (EST)
References: <200702152136.l1FLadHQ023698@mail.rootsweb.com><REME20070215200659@alum.mit.edu><79d120de0702151735q594ddd9ftc62123b920676e9d@mail.gmail.com>
In-Reply-To: <79d120de0702151735q594ddd9ftc62123b920676e9d@mail.gmail.com>(adam.bradford@gmail.com)


Adam wrote:
> I was completely unaware that this rounding confusion was a possibility.
> Does this apply to all markers or only certain ones?

Please note, first of all, that non-integer alleles are rare. Thus,
rounding itself is rare. Rounding ambiguity would occur only when
the allele is exactly half-way between two integers, and therefore
only when the repeat motif length is an even number. The commonly
used markers have motif lengths of 2, 3, 4, and 5. 4 is the most
common. You can look up these lengths on the SMGF web site (under
Marker details). A consistent scheme of rounding would need to
round first to the PCR product length in base pairs, and only then
to round to the nearest multiple of the motif length, using an
agreed-upon rule for resolving the halfway values. I have no idea
whether the Arizona lab does it this way or instead does the
rounding directly from the raw measured lengths to the motif
multiples.

John Chandler

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