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Archiver > GENEALOGY-DNA > 2010-02 > 1267372475


From: "Ken Nordtvedt" <>
Subject: Re: [DNA] : low variance MRCA dates for P310cladesin ItalyandSEEurope
Date: Sun, 28 Feb 2010 08:54:35 -0700
References: <201002280813.o1S8DmoN029265@mail.rootsweb.com>,<004601cab88c$725955f0$5e82af48@Ken1><SNT115-W42BD3E0D6573C3B61EAB55CC3D0@phx.gbl>


----- Original Message -----
From: "Steven Bird" <>


Ken, the distinction between the "coalescent" and TMRCA is an artificial
one. The published literature widely refers to these terms as
interchangeable. That is, unless you are redefining them...

Steven Bird, DMA

Gee, that was snotty for so early in the morning. Perhaps you are out of
coffee?
Coalescence age of a tree and the TMRCA are two different things, as are
their estimates.

TMRCA is what it says --- age back to the single male who is the most recent
common ancestor of all the N sample haplotypes.

Coalescence age is the average tmrca of each of the N(N-1)/2 pairs of
haplotypes taken from the N sample haplotypes. Due to the collapsing
structure of the tree going back in time, most of those haplotype pairs have
their tmrcas at nodes more recently than the TMRCA of the whole set. So
Coalescence age is necessarily younger than TMRCA.

The mathematical expressions for the two things are also different --- the
TMRCA expression requires an inference or guess as to the founding
haplotype, while the coalescence age expression does not as it is doing
tmrcas between pairs of known present haplotypes




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