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Archiver > GENEALOGY-DNA > 2010-03 > 1269707947


From: (John Chandler)
Subject: Re: [DNA] Family Finder Test
Date: Sat, 27 Mar 2010 12:42:58 -0400
References: <971b.3ff82e9.38df5280@aol.com><SNT132-w336D1596AD25C9B4A58E28C0220@phx.gbl>
In-Reply-To: <SNT132-w336D1596AD25C9B4A58E28C0220@phx.gbl> (message fromElizabeth Bennett on Sat, 27 Mar 2010 11:07:30 -0200)


Elizabeth wrote:
> If autosomal results could indicates cousins of some degree and they
> are assumed to be cousins through their paternal lines, can these
> results be used to group Y DNA test results in smaller group within
> a large one to help develop a phylogenetic tree? It is not a case
> of one of the other autosomal or Y-DNA but can they be used in
> combination.

Here's an example of autosomal results indicating cousins of some
degree: eye color. It's quite true that, all else being equal, the
blue-eyed testees are more closely related to each other than they
are to the brown-eyed testees, and vice versa. We could certainly
gather data on the eye color (or blood group) of our project members
and use those data to form clusters by simply assuming the relationship
to be on the paternal side. However, there is no justification for
that assumption. The same is true of Family Finder.

Sometimes, I think that genetic genealogy (as practiced heretofore) has
been a serious setback to genealogy as a whole. GG has fostered a very
unhealthy "shorthand" notation that refers to people being "not at all
related" when the truth is that they merely have very different Y
chromosomes. For example, if my own maternal grandfather were alive
today and joined the Chandler DNA project because he heard me talking
enthusiastically about it, the results would show that "we are not at
all related" in the terminology of genetic genealogy. And yet a
Family Finder or 23andMe test would reveal that we share something like
1/4 of our DNA -- perhaps even more. The key here is that autosomal
testing carries the same criteria for relationships as in traditional
genealogy, but the range of detection is strictly limited by the rapid
fall-off of consanguinity (factor of 2 for each generation up the tree
to a common ancestor and for each generation back down the other branch).

When you step over from haploid genealogy to diploid, it is necessary to
shed the shorthand and get back to thinking more like a traditional
genealogist.

John Chandler


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