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Archiver > GENEALOGY-DNA > 2005-03 > 1111729510


From: (John Chandler)
Subject: Re: [DNA] Re: Cryptic Backup Copy of Genome - "Hothead Gene"
Date: Fri, 25 Mar 2005 00:45:10 -0500 (EST)
References: <4242410D.2020909@comcast.net>
In-Reply-To: <4242410D.2020909@comcast.net> (message from Bonnie Schrack onWed, 23 Mar 2005 23:24:45 -0500)


Bonnie's father wrote:
> > case of DNA. Say there is a particular energy associated with a bond
> > in the DNA. The higher the temperature the greater the rate of
> > temperature induced mutations. But what if the mutation is caused by
> > something that has sufficient energy to make a bond with higher
> > energy than the original DNA structure ( like say -- radiation) . Then
> > the new arrangement might well "disintegrate" back to the original
> > un-mutated structure in time.

The key point about DNA mutations is that there are no "single-point
failure modes." In other words, it takes more than one zap to convert
any one DNA base into any other. Indeed, it's hard to imagine
changing a G or an A into a C or a T with any sequence of random
zaps. Further, the DNA repeair mechanism is capable of correcting a
zapped base irrespective of the energy levels, but this can only work
in the short term. If you zap the DNA of a cell that is dividing,
such that the mutation is passed on to one of the daughter cells, then
it becomes a lot harder to undo the damage -- only the other
chromosome with its possibly different copy of the same sequence can
intervene through recombination.

The explanation of the apparent gene reversion has to be either
something simple (like mixed-up samples) or something weird (like
reverse copying from leftover RNA lurking somewhere in the cell).

John Chandler


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