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Archiver > GENEALOGY-DNA > 2008-05 > 1210973340


From: "Ken Nordtvedt" <>
Subject: Re: [DNA] age of U152/S28
Date: Fri, 16 May 2008 15:29:00 -0600
References: <376415.68533.qm@web86614.mail.ird.yahoo.com>


This is what trees with as many of the nodes (MRCAs) dated for age as
possible do --- confine SNPS between a node prior to their existence and
after their existence. But why do you want SNP ages? (I can answer my own
question but I won't at the moment). The dates of the nodes are the
important thing.

Ken
----- Original Message -----
From: "Alan R" <>
To: <>
Sent: Friday, May 16, 2008 9:49 AM
Subject: [DNA] age of U152/S28


> The discussion about the difference between the MRCA date and the date of
> the mutation is interesting. The distinction is clear but I am worried
> that the real date of the arrival of a clade like S28 is wrongly taken by
> many to mean how old S28 is. Its easy to see a scenario where daughtering
> out etc means that the MRCA can be much more recent than the mutution.
> MRCA is therefore the minuimum possible age of a mutation and this minumum
> may be wildly younger than the mutation date. In other words MRCA is what
> archaeologists call the 'terminus anti quem', the date before which
> something simply must have existed. However, if you dont have the reverse
> (terminus post-quem) then its use is limited. Can MRCAs be calculated for
> a sub-sub clade, a sub clade then the clade as a whole then the haplotype
> as a whole way to sort of 'squeeze' a mutation dating band? For example
> S28, all western R1b1c, all R1b1c, all R1b.
>
> Alan
>
> PS can the effect of daughtering out etc be computer simulated to allow a
> calibration of MRCA dates into mutation dates?
>
>
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