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Archiver > GENEALOGY-DNA > 2004-02 > 1076433704

From: "Mark MacDonald" <>
Subject: RE: [DNA] DAVIDSON CLAN ORIGINS - MacPHERSON or COMYN
Date: Tue, 10 Feb 2004 11:21:44 -0600

John
How many more generations to get a 96% confidence rating within 7
mutations of a common ancestor with 25 markers? With 37 markers? This
is not a hypothetical; I have a real population in mind. Thank you: I
don't have the math skills myself.
Mark MacDonald
-----Original Message-----
From: [mailto:]
Sent: Wednesday, February 04, 2004 9:36 PM
To:
Subject: Re: [DNA] DAVIDSON CLAN ORIGINS - MacPHERSON or COMYN

Len wrote:
> Just wondering how generous I should be, given
> present interpretation guidelines. How would 5 to 9 genetic distance
sound for
> MRCAs 1000-1500 years ago?

If you can identify the ancestral haplotype (and you really need to),
you can then compare each test subject against the ancestor. That
means you can tighten up a bit. Figuring 60 generations in 1500
years and a mutation rate of 0.002, I get 96% chance that 6 or fewer
mutations will have occurred in any individual. If you want to take
two-step mutations into account, then the concept of genetic distance
become much more complex. You would want to allow for any
combination with a reasonable shot at appearing in 60 generations,
i.e., in terms of how many markers differ by 0,1,2,3:

25-0-0-0
24-1-0-0
23-2-0-0
22-3-0-0
21-4-0-0
20-5-0-0
19-6-0-0
24-0-1-0
23-1-1-0
22-2-1-0
21-3-1-0
20-4-1-0
23-0-2-0
22-1-2-0
21-2-2-0
20-3-2-0
22-0-3-0
21-1-3-0
24-0-0-1
23-1-0-1
22-2-0-1
21-3-0-1
20-4-0-1
23-0-1-1
22-1-1-1
21-2-1-1
22-0-2-1
21-1-2-1
23-0-0-2
22-1-0-2

I haven't done any calculations for four-step differences, but those
could occur too.

John Chandler

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