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Archiver > GENEALOGY-DNA > 2007-02 > 1171464041


From: Vincent Vizachero <>
Subject: Re: [DNA] TMRCA
Date: Wed, 14 Feb 2007 08:40:41 -0600
References: <KHEKIJEABJGJEKDPFEDMIEMDDDAA.elizabethod@eircom.net>
In-Reply-To: <KHEKIJEABJGJEKDPFEDMIEMDDDAA.elizabethod@eircom.net>


On Feb 14, 2007, at 7:46 AM, Elizabeth O'Donoghue wrote:

> There appears, to me at least, to be no common
> agreement within the profession of appropriate calculation methods,
> nor does
> there seem to be any mad dash to reach one. Shouldn't this be one
> of the
> fundamental goals of the genetic genealogy community?

First, I don't think the situation is so dire as some have have
suggested.

TMRCA calculators are designed to determine the probability that two
people share a common ancestor in a given amount of time. In a
genealogical context, they typically perform pretty well when used as
intended. There are some differences in opinions about what mutation
rate estimates are appropriate, but those differences are pretty
minor for the established STR markers and tend not to have dramatic
effect on the resultant estimates. All the calculators I use produce
an estimate that includes a time period and an associated
probability, which makes interpretation relatively straightforward.

Estimating the haplotype of the common ancestor is likewise a
straightforward process if (and it is a big if) you can collect
enough data. If the common ancestor lived long ago, getting tests
from all the appropriate lines of descent can be a huge challenge for
most surname projects.

Estimating the ages of haplogroups or subclades is much more
perilous, of course, for a whole host of reasons. There are several
methods for working around the limitations inherent in producing such
estimates, not all of which are appropriate for every circumstance.
Unfortunately, this is not a problem for which a consensus solution
can be forced.

Vince

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