Hello,
The following was posted on the ISOGG (International Society of Genetic Genealogist) web.
I think it is appropiate to post on this forum. I am posting in its entirety.
John R. Carpenter
La Mesa, CA
Date: Mon, 31 Oct 2005 00:26:58 -0500
From: John <scottish_dna(a)comcast.net>
Subject: Y-DNA Testing - What can do and what it can't do
With all the discussion about Triangulation Method vs. Phylip
diagrams and Fluxus diagrams I think many of us are losing sight of
what Y-DNA testing is all about and what it can and cannot do for us.
Testing DNA is a very exact science and extremely reliable and
accurate. Test results themselves are almost always correct. But what
do the test results mean? By themselves they mean very little. It is
only by comparing them to other test results that they take on any
meaning for genealogists. The only way to derive information by
comparing test results is to make assumptions and use statistical
analysis. Mutation rates are a key component of computing TMRCA but
no one really knows what the mutation rates are and there are several
different estimates of the average mutation rate. There are also
different ways of counting mutations and each produces it's own
TMRCA. Statistic analysis by it's very nature can only provide a
range of probabilities. All these factors introduces a great deal of
uncertainty into the analysis of DNA test results. So where does that leave us?
Y-DNA testing is just another tool to be used by genealogical
researchers. A tool to help us support or refute existing paper
trails, break through brick walls, and hopefully connect and steer
researchers in the right direction. Y-DNA testing cannot prove a
relationship though it can certainly provide compelling evidence to
support one and can certainly disprove a relationship. Y-DNA testing
cannot establish a most recent common ancestor but it may provide
some information on when this common ancestor might have existed.
As project administrators we recruit participants, have their DNA
tested, try to interpret their test results, and try to connect the
participants to other participants. In some cases this may be quite
straight forward as when two participants believe they share a known
common ancestor or when it is believed that two ancestral lines are
related and the test results confirm or refute this belief. In other
cases it is far more difficult as when participants with no known
relationship match closely on the DNA test results. As project
administrators it is only natural that we what to "prove" a
connection, find the common ancestor, or at least compute the
ancestral haplotype of the common ancestor. So we turn to all the
tools of Y-DNA testing: triangulation, Phylip diagrams, and Fluxus
diagrams. But in reality what do these really get us; a theoretically
haplotype or a hypothetical diagram which may or may not depict the
truth. Does any of this really bring us any closer helping the
participant realize his real goal of furthering his genealogical tree?
Without a well documented paper trail the best DNA testing can do is
help point participants in the right direction in continuing their
research. Participants who closely match on their results can combine
their efforts, compare notes, and work together to further their
research. The answers, in the end, will only be found through
conventional research.
While it might be of great satisfaction for the 30 participants in my
Group 1 to know they most likely descend from the "original" Blair of
Blair back about 1200, this knowledge is of little value to the
participant who's paper trail ends in Laurel Co., KY in 1800.
Scottish DNA - Better than Life Insurance
John
-----
John A. Blair
Goffstown NH
http://blairgenealogy.com
mailto:dna@blairgenealogy.com
BLAIR DNA Project Coordinator