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Archiver > GENEALOGY-DNA > 2007-10 > 1191272687


From:
Subject: [DNA] mutation rate and TMRCA [was Re: East Anglia and the Vikings]
Date: Mon, 1 Oct 2007 17:04:47 EDT


In a message dated 10/1/2007 12:49:59 PM Pacific Daylight Time,
writes:

> John, I've seen you and probably others make this statement periodically.
> I
> don't have the mathematical skills to easily test what difference there is
> between TMRCA based on 'slow' vs fast' markers, but Family Tree does set
> their calculator to take into account the varying mutation rates of each
> marker when comparing individuals. I have seen where the GD of two
> individuals varies, even if they have the same genetic distance but at
> different markers. On occasion, I've seen a closer TMRCA for two
> individuals with a greater genetic distance than two with a lesser distance
> (granted it's usually just a difference of one). And it's not hundreds of
> years, but it could be more than a hundred, even within a genealogical time
> frame.

One thing to bear in mind: the FTDNATiP report is based on number of
mismatches, not Genetic Distance. For example, I have two unrelated people in my
project with a Genetic Distance of 17, but the report is based on 9 mismatches. If
one person has say 22 for DYS390 and the other has 25, that would count as one
mismatch (the "infinite allele" model). I'd be surprised if you located an
example where people with two mismatches ended up closer than people with one
mismatch.

http://www.ftdna.com/faqtip.html#q1.7

You can play with effect of changing fast vs slow markers at SMGF, which also
uses the infinite allele model. Start with a perfect match, then change the
query to make varying numbers of mismatches and varying genetic distances.
Click on the TMRCA button to see how much difference it makes. You'll find that
people who differ on two slow markers have a more recent common ancestor than
those who differ on fast markers, although the difference is very slight. If you
don't have a starting point of your own, you can use the query for my husband
Jim (not the same Jim Turner that posts here!).

http://tinyurl.com/y93udg

I don't know whether SMGF has updated its mutation rates since this 2004
poster, but the rank order of fast to slow should be roughly the same:

http://www.smgf.org/resources/papers/ASHG2004-4.pdf



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