GENEALOGY-DNA-L ArchivesArchiver > GENEALOGY-DNA > 2007-06 > 1182448988
From: "Peter A. Kincaid" <>
Subject: Re: [DNA] TMRCA Corrections
Date: Thu, 21 Jun 2007 15:03:08 -0300
I am just looking at possible application of this
in relation to surname projects. For surnames
that are territorial in origin there is the implied
common ancestor - the person who assumed
the name of the lands he held. Many cases this
assuming took place 600 plus years ago. However,
most participants can only trace their ancestry back
two to three hundred years ago. Looking at
TMCA figures generated the traditional way
one tends to call into question a figure in excess
of say 1000 years. You noted that some outliers
could have their TMRCA inflated. I'm was trying
to get a sense of what a point of no return might
be in terms of who should be in a cluster.
----- Original Message -----
From: "Ken Nordtvedt" <>
Sent: Thursday, June 21, 2007 1:31 PM
Subject: Re: [DNA] TMRCA Corrections
> First, non paternal events are genealogists' problems, not mine (or at
> I don't think I have such a concern). They have nothing to do with
> adjusting TMRCA if you know the relationship of a pair of haplotypes to
> ancestral clade in which they live.
> I ran my calculations back 25 generations to cover the bulk of
> applications. So your 30 generations is a similar thing.
> So I am calculating the change in the generation dependent probability
> for the MRCA back the most recent 25 generations, given that the haplotype
> pair at issue resides in the descendant population of a clade whose
> lived 150, 250, 400, etc. generations ago.
> In principle, I guess, we could run the same thing for a clade consisting
> descendants of Genghis Khan, i.e. a clade itself only 30 or 40 generations
> old. Or Henry the 8th, or even some prolific but difficult to connect
> dynasty founded in early New England.
> ----- Original Message -----
> From: "Peter A. Kincaid" <>
> To: <>
> Sent: Thursday, June 21, 2007 10:12 AM
> Subject: Re: [DNA] TMRCA Corrections
>> If we take 30 years to a generation then most surname
>> projects are dealing with a timeframe of within 30
>> generations. Thus, it seems that you are suggesting
>> that the TMRCA correction would be quite significant
>> (given the increase going from 400 G to 150 G) for
>> anyone testing for genealogical purposes. Furthermore,
>> if the pattern for 200 generations is comparable
>> for 30 generations then, within a surname cluster, an
>> outlier's TMRCA could potentially be overstated.
>> Either that or there is no application to surname projects.
>> The whole concept does not help one decide at what
>> point, in terms of mutations from the node of a cluster
>> within a surname project, is a non paternity event the
>> likely scenario.
>> ----- Original Message -----
>> From: "Ken Nordtvedt" <>
>> To: <>
>> Sent: Thursday, June 21, 2007 1:14 AM
>> Subject: Re: [DNA] TMRCA Corrections
>>> ----- Original Message -----
>>> From: "John Chandler" <>
>>> This means that the
>>>> tables for cases even just a few steps away from modal will have
>>>> to be carefully calculated with proper weighting. I hope you are
>>>> proceeding with these calculations, or at least a sample.
>>> Here's an illustrative sample case. m = .0025 Clade 200 generations
>>> I considered two identical haplotypes but displaced from the founder's
>>> haplotype by one step mutations at fraction F of its markers. Below I
>>> the rescaling of the (mean)TMRCA and accompanying percentile confidence
>>> boundaries for various values of fraction F of one step mutations from
>>> central founder's haplotype.
>>> F = 0 161%
>>> F = .2 123%
>>> F = .4 100%
>>> F = .6 84%
>>> So the tendency of TMRCAs moving from greater than traditional values
>>> TMRCA to less than traditional values for TMRCA as one's haplotype pair
>>> moves away from the founder's central haplotype is being carried out.
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|Re: [DNA] TMRCA Corrections by "Peter A. Kincaid" <>|