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Archiver > GENEALOGY-DNA > 2005-07 > 1122838368
From:
Subject: Re: [DNA] FTDNA Genetic Distance Calculations & Assignment to Family Groups
Date: Sun, 31 Jul 2005 15:32:48 EDT
In a message dated 7/31/2005 12:55:40 P.M. Central Daylight Time,
writes:
IF ANYONE HAS A BETTER - more user friendly - explanation - or knows of one
on the web
I certainly don't! I have bookmarked this and intend to put a "Technical
Discussion" article in an upcoming issue of my Project Newsletter referring to
your page. I would make one suggestion -- that you add a blurb on some of the
criteria Group Administrators use to assign folks to a group.
1. Sharing of an unusual allele for their haplogroup combined with the same
surname and a match within the probability distribution for the number of
markers. That is, while 12-50 markers have a 90% or better probability of
having NO mutations, 1-3 mutations also carries a non-zero probability of
occurring, on any ONE man. Therefore, as John Chandler and others have pointed out,
we can have documented cases in which the comparison of two men who happen,
by chance, to each have 1-3 mutations can result in these two men showing 1-
6 mutations. And the more generations they are separated the larger that
"extreme number" of mutations can grow.
Therefore unless there is a BETTER match on the number of tested
matches, Group Administrators may put a person in a group that is the "best
available match at present." It may be that a future testee will be found whose DNA
is midway between the two and "splits the difference." Or a future testee
may come in who is a better match and the original person will be reassigned to
a different group. This science is still evolving and we are still learning.
2. Membership in a shared sub-sub clade with the same surname and match
within the realm of probabilities. For example, three men who share the
characteristics marker alleles usually found in I1a "Anglo-Saxon variety" are more
likely to be related to one another than to a man with the characteristic
marker alleles of I1a "Norse" variety, even if they have more than expected the
number of mutations between/among them.
3. Paper trail clues -- all born in NC in one decade, moving in similar
migration paths, marriages to the same related surnames, etc. or whatever paper
trail evidence suggests a possible MRCA, including unusual names or shared
middle names for which there is no obvious explanation (i.e., all three show
the middle name Day, but there is no known marriage in any to a Day family but
all have LNU wives once you get back to 1790s.
4. Some combination of these factors.
Anne
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