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Archiver > GENEALOGY-DNA > 2005-08 > 1123268751


From: (John Chandler)
Subject: Re: SMGF [was Re: [DNA] FTDNA Genetic Distance Calculations...]
Date: Fri, 5 Aug 2005 15:05:51 -0400 (EDT)
References: <IGEOKAGLHNEKPCKPADIGOEIKKEAA.bbailey.lowedna@baileyconnection.com><REME20050803190044@alum.mit.edu> <6.0.0.22.0.20050805102153.06137ba8@wells.org>
In-Reply-To: <6.0.0.22.0.20050805102153.06137ba8@wells.org> (message fromOrinWells on Fri, 05 Aug 2005 10:35:28 -0700)


Orin wrote:
> We also have one example where we know that
> an individual had two mutations, however one of them was not passed on. We
> would not have known this if we hadn't coincidentally tested individuals in
> three generations in this family.

The term for this is "somatic mutation". By taking a buccal DNA sample,
you don't actually determine the state of the germ-line cells. The same
is also true of a blood sample. However, if you did both a blood test
and a buccal test and found a disagreement, you would know that there
was either a lab error or a somatic mutation somewhere.

> Now THIS introduces an interesting possibility. Most discussions on
> mutations have been predicated on the belief that once a marker mutates
> that this mutation will be passed on from there on out. This may not be
> true. We really have no studies to show this.

Yes, we do. People have tried to measure the mutation rate
independently using father-son studies and pedigree studies. If there
were a substantial fraction of germ-line mutations that revert in the
next generation, the results of father-son studies would show
substantially higher mutation rates than pedigree studies. They do
not. Therefore, we can rule out "reversion" as a major factor.

John Chandler

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