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Archiver > GENEALOGY-DNA > 2002-11 > 1037738220


From: "John F. Chandler" <>
Subject: Re: [DNA] MRCA calculations
Date: Tue, 19 Nov 2002 15:37 EST
In-Reply-To: DNACousins@aol.com message <11c.1a9c3dc3.2b0bbf59@aol.com> of Tue, 19 Nov 2002 09:23:17 -0700


Ann wrote:
> Not too much different, though. My MRCA calculator (based on Walsh's
> equations, which assume a one-step difference) gives a value of 26.8
> generations. Walsh also discusses what he calls the stepwise mutation model
> (SMM), and his conclusion was that it wouldn't make much difference over a
> "short" time scale. If I am interpreting his formula on page 906 of his paper
> correctly, he would define "short" as < 250 generations. Would you check that
> for me?

Yes, that's what he was saying, but his underlying statement (that "most"
loci would have no more than one mutation on that time scale) is a little
bit of a stretch. It comes to 73%. Anyhow, that's approximately the
scale. If you set the cutoff as < 133 generations, then 90% of the
loci would have no more than 1 mutation (bearing in mind that there are
two lines being compared here).

John Chandler

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