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From: "Anatole Klyosov" <>
Subject: Re: [DNA] Variance Assessment wrt back and parallel mutations
Date: Thu, 11 Feb 2010 22:20:45 -0500
References: <mailman.4304.1265934440.2099.genealogy-dna@rootsweb.com>


>From: "Alister John Marsh" < >

>Sasson,

>You said...
>>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%".

>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.

My response:

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
error). At 3000 years they subtract 12%, still commonly within typical
margins of error. At 5000 years they decrease TMRCA by 20%. At 10,000 ybp
they subtract 39% from TMRCA. At 28,000 years they show only 50% of the
TMRCA. At 50,000 years they show only 770 generations when in fact it should
be 2,000 generations.

>If he has allowed for the fact that most mutations occur on a subset of
markers that mutate about once every 50 transmissions, then Anatole is
probably right that back mutations are seldom significant in shorter time
frames.

It does not matter, whether mutations occur every 50 transmissions, or every
5, or every 1000. We talk about a "contribution", which is a fraction of the
total. Back mutations are absolutely insignificant in time periods of family
studies.

>In the case of my example which Anatole analyzed, he gave an estimate of
>100 years to MRCA of two persons. One of those persons was born about 90
>years ago, and is no longer living.

I gave it 140+/-140 years. It was just one mutation between two 37 marker
haplotypes. I do not think that it is a serious matter to even discuss it.
Clearly that the common ancestor lived rather recently.

The whole exercise shows that there is nothing "mysterious" in mutation
calculations and interpretations. They obey rather clear and understandable
rules. It is us who complicate things, not mutations.

Regards,

Anatole Klyosov



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