Critical rate of mutations

Cameron Neylon camn at
Mon Jun 13 20:23:16 EST 1994

szeinfel at FOX.CCE.USP.BR (Rafael N Szeinfeld) writes:

>	By increasing genome size you decrease the probability of a 
>mutation happens at a vital locus.

I know this is accepted wisdom but is it actually true. It depends on
the main mechanism of mutation. If most mutattions (or at least
important ones) occur through errors in replication, then increasing the
genome size merely increases the number of errors. 

In fact under any circumstances where any base pair has a percentage
chance of being altered then changing the genome size will have no
effect in prtoecting vital loci.

If, however there are a certain 'number of mutagens per cell',
presumably chemical or physical effects, then increasing the genome size
_will_ tend to lower the overall mutation rate (in terms of per base)

Of course, in real life there will presumably be a combination of both,
and increasing genome size may be an adaption to environmental mutagens
or mutagens that occur at a certain rate per cell. It will never protect
against errors in replication.

What is teh main mechanism of mutation?

Cameron Neylon, Honours, Dept of Biochemistry,
University of Western Australia

(09) 368-2717 or more regularly camn at

Biochemistry: noun, The art of sitting, late at night, transferring 
              ridiculously small volumes of liquid with one hand and
	      attempting to hold onto one's sanity with the other.

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