> It can also change if the cellular environment changes. The presence of
> chemical mutagens in the cell will change the mutation rate. Not to
> mention X-rays or even UV light. A reduction in the ozone layer could
> conceivably increase mutations significantly.
True, but that's because mutagenesis is an "artificial" form of mutation
compared to the normal way mutation occurs, ie replication errors. The rate
of mutagenesis is directly proportional to the amount of mutagenic agent
present; as the amount of mutagenic agent increases or decreases, mutagenesis
increases or decreases. The rate of mutation on the other hand is determined
solely by how often a replication error occurs, which can vary from place to
place in the genome, but otherwise is fairly constant in any one location.
Kevin L. O'Brien