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Archiver > DNA-R1B1C7 > 2008-02 > 1203226263


From: "David Ewing" <>
Subject: Re: [DNA-R1B1C7] Age of R1b1c7
Date: Sat, 16 Feb 2008 22:31:03 -0700


In this thread we have been discussing how we might use the increasingly
large number of R1b1c7 37-marker haplotypes available to estimate the age of
R1b1c7. I don't pretend to have the answer to this, but thought it might be
useful to share my thinking about the problem with the list--I would welcome
having any fuzzy logic or mistaken notions pointed out to me. I have copied
this posting also to John McEwan and Ken Nordvedt, both of whom have
considerable experience in these matters, in hopes that they would be
willing to instruct us in this a bit.

The average of Chandler's (http://www.jogg.info/22/Chandler.pdf) estimated
mutation rates for the 37-marker FtDNA panel is 0.00492. If we eliminate the
two CDY markers from consideration, the 35-marker average is 0.00318. [And
if we eliminate all five markers with mutation rates >.008, the average rate
for the remaining 32 is .00265. The average rate for the slowest 23 markers
(those with rates <.004) is 0.00148. I have thought that this kind of
calculation should somehow favor slower moving markers, but Ken Nordtvedt
has argued that this is a mistake. Sadly, I can't remember his rationale,
though I found it convincing at the time.]

For the sake of argument, let us accept a date of 450 AD for Nial of the
Nine Hostages, which is 1558 years ago. At 30 years per generation, this is
52 generations. Now, I understand that predicting mutations in the usual way
is fraught with some peril when using time intervals this large (is this
because back mutation becomes a significant factor, or for some other
reason--genetic drift, perhaps?), but let us see what happens if we use Ann
Turner's mutation calculator. You can download this from
http://members.aol.com/dnafiler/MutationCalculator.exe
or if you are afraid of the .exe file, you can read about it first at
http://archiver.rootsweb.com/th/read/genealogy-dna/2002-11/1037233627.

Enter 35 markers, 0.0032 mutation rate and 52 transmission events. This
yields 5.8 "expected mutations," distributed (Poisson distribution) roughly
as follows: 0.3% of Nial's 50th great-grandsons will have zero mutations,
1.7% will have one mutation, 5% will have two, 9.7% will have three,
14.2%will have four,
16.5% will have five, 16% will have six, 13.3% will have seven, 9.7% will
have eight, 6.3% will have nine, 3.7% will have ten, 1.9% will have eleven,
less than one percent will have twelve, etc, etc. So "on average" his
descendants will be genetic distance six or seven from the modal, and those
of his 50th great-grandsons for whom he is the most recent common ancestor
should be at an average genetic distance of fifteen or so from one another
(because two such great-grandsons would be separated by 104 transmission
events). Remember, I am leaving CDYa/b out of consideration, here.

My impression is that the "diversity" of R1b1c7 is not this large, though I
don't know of any data that systematically analyzes FTDNA 37-marker panels,
excluding the CDY markers. Does anyone have a simple way to tablulate the
genetic distances between a large number of R1b1c7 haplotypes or to
calculate an average of such? One potential problem in taking this approach
would be to include too many close relatives, because this would understate
the average difference. Maybe we could get around that by just using R1b1c7
surname modal haplotypes rather than considering all the individual
haplotypes we can find.

David Ewing

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