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Archiver > GENEALOGY-DNA > 2002-11 > 1037563620


From: "John F. Chandler" <>
Subject: Re: [DNA] MRCA calculations
Date: Sun, 17 Nov 2002 15:07 EST
In-Reply-To: DNACousins@aol.com message <f3.24249ad1.2b091ccd@aol.com> of Sun, 17 Nov 2002 09:24:47 -0700


Ann wrote:
> I checked your formula against Bruce Walsh's tables for 20 and 50 markers. It
> looks like your formula underestimates slightly, more and more as D
> increases. But I think this would be a good ball-park formula for cases where
> we don't have any tables.

Actually, my formula gives an OVERestimate. I think Walsh's tables
give values for the number of loci that match vs do not match. Thus,
if you read his table to get the time for n=20 and k=19, you are getting
a superposition of cases with D=1, D=2, D=3, etc., where only one locus
is affected. This superposition increasingly makes the two quantities
diverge as k decreases and D increases.

John Chandler

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