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From:
Subject: Re: [DNA] How do you do an estimated Common ancestor
Date: Wed, 14 Feb 2007 07:52:13 EST


In a message dated 2/13/2007 11:23:45 PM Pacific Standard Time,
writes:

> You need to find the genealogical connections here through the old
> paper trails. Trying to figure out from 3 differences how far back
> they are related is a waste of time in my humble opinion no matter
> how many on this list still want to find a way for that to
> work. Again I can show you cousins 500 years from their common
> ancestor who have no differences and two brothers who have three. I
> just have no confidence in these MRCA calculations. You are working
> with mother nature at her random best with mutations.
>

But Orin ... that is exactly what MRCA calculations tell you to expect: some
percentage of brothers will differ, and some percentage of 10th cousins will
be identical, due to the random nature of mutations. MRCA calculations cover a
range of probabilities, and they're best used as a sort of triage: it's
worthwhile pursuing genealogical evidence, or it's not worthwhile, or it's
borderline and more DNA testing (more markers or more people) might tip the scale one
way or the other.

Ann Turner

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