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Archiver > GENEALOGY-DNA > 2011-01 > 1294160143
From: "Ken Nordtvedt" <>
Subject: Re: [DNA] How old is Y-Chromosome Adam?
Date: Tue, 4 Jan 2011 09:55:43 -0700
References: <201101040808.p0488xgP020485@mail.rootsweb.com><AA814106-788F-475B-9494-D839E21F7AC6@vizachero.com><AANLkTi=FN3NEtEsp93qpYyLSr_tD9PLJb+pRZm+HHpv7@mail.gmail.com>
The expected values of probability distribution for a marker's mutation rate
is what one should take from some measurement procedure's data --- not most
likely value (peak of distribution). This is because it is the expected
(average) values of distributions which go into the central limit theorem,
not the most likely (peaks) values of distributions.
In a typical measurement procedure a very large number N of father/son
transitions are looked at, and a marker is seen to mutate n times. The most
likely inference of rate is then n / N, while the average value of the
inferred distribution for mutation rate is (n+1) / N
Choosing n rather than n+1 leads to systematic underestimation of marker's
rate of about 1/N which for the very slowest markers has tended to be
comparable to the inferred rate.
This gets a little bit more complicated in measurement procedures destined
to just yield relative rates. In that case a marker's fractional rate
compared to the sum of all markers should be:
m(i) / M = (n(i)+1) / Sum over all j of (n(j)+1)
rather than
m(i) / M = n(i) / sum over all j of n(j)
This also systematically underestimates rates for slow markers but
overestimates rates for fast markers. Then when you restrict yourself more
and more to a subset of the slowest markers you enhance the fractional bias
of your total M of markers used.
----- Original Message -----
From: "Dienekes Pontikos" <>
To: <>
Sent: Tuesday, January 04, 2011 9:17 AM
Subject: Re: [DNA] How old is Y-Chromosome Adam?
What is the basis for the suspicion that slow markers are overestimating
TMRCA?
On Tue, Jan 4, 2011 at 4:54 PM, Vincent Vizachero <>
wrote:
> But given the very
> real suspicion that the very slowest markers may be overestimating
> TMRCA, an estimate formed ONLY on those markers would - itself- strike
> me as suspicious.
>
> VV
>
--
Dienekes' Anthropology Blog: http://dienekes.blogspot.com
Dodecad Ancestry Project: http://dodecad.blogspot.com
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| Re: [DNA] How old is Y-Chromosome Adam? by "Ken Nordtvedt" <> |