GENEALOGY-DNA-L Archives

Archiver > GENEALOGY-DNA > 2006-08 > 1155354495


From: "Lawrence Mayka" <>
Subject: RE: [DNA] a new model for TMRCA
Date: Fri, 11 Aug 2006 22:48:15 -0500
In-Reply-To: <44DC9D20.7060908@charter.net>


> From: John Lerch [mailto:]
> I.E. suppose the haplogroup I'm
> looking at has 400 members and I'm comparing 40 markers, then
> there are
> typically 10 that are as near or marginally nearer than the modal. I
> take this to mean that (geometrically) we all are moving away
> radially
> from any particular ancestor (If it seems like we're not, we
> can find a
> new set of axes in which we are.)

'Modal' does not equal 'ancestral'. One could say that each rapid
population expansion results in a subgroup whose modal is the ancestral for
that subgroup. But if a given haplogroup is thousands of years old, various
segments of its population have undergone various rapid population
expansions, each of which has its own modal; and hence the radial movement
you mention may result in two subgroups moving *toward* each other. (A
better phrasing is that over time, random mutation will cause the two
subgroups to overlap more and more, and it then becomes increasingly
difficult to distinguish the two.) The net effect is that a subgroup's
haplotype behavior is most affected by its most recent population expansion,
whether or not an SNP is available to segregate that particular expansion.

If we could find an SNP corresponding to each rapid population expansion
throughout human history, we could separate out all these subgroups and
perform interesting calculations on them separately. But alas, we have not
found nearly enough SNPs for that.



This thread: