Archiver > GENEALOGY-DNA > 2010-02 > 1266001731

From: "Lancaster-Boon" <>
Subject: [DNA] Variance Assessment wrt back and parallel mutations
Date: Fri, 12 Feb 2010 20:08:51 +0100

Dear Anatole

This helps me, but it also explains some confusion!

>>1) Regarding the issue of "back/parallel mutations", I think Anatole's
methods do not simply ignore the issue, but account for it in some
simplified way, so that for 800 years or so there is no problem, and for
longer periods there is a "correction formula". So it seems to me, you
cannot simply "add 10%".

"Alister John Marsh"
>I was essentially asking the question of Anatole, did he calculate that
back mutations were insignificant on the assumption that all markers had
equal mutation rates, or did he allow for the fact that most mutations occur
on a small subset of very fast mutating markers. I await Anatole's response
to that.

There was no assumption except a statistical, random nature of mutations.
The exponential formula for a gradual significance of back mutations with
time is applicable to any single locus, fast" or "slow", and to averaged
loci as well. Back mutations are insignificant being compared to "forward"
mutations during the first 600-800 years, and practically to the first 2000
years (being within 8% for the 2000 ybp mark, that is well within margins of

What this apparently means is that you know you are not really "counting
mutations", and it becomes a question of how good your approximation is.
(And of course you may well be right.)

I believe I am right to say however, that this is what several of your
interlocutors have been saying, to your strenuous disagreement. Perhaps you
did not fully take in what people were saying sometimes.

Best Regards

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