> There is a fallacy in these arguments, namely that the number of mutagenic
> hits PER GENOME is constant. It seems more likely that the number of
> mutations per base pair is fairly constant. Therefore adding more "junk"
> would not dilute out the critical targets, it would only increase the
> number of mutation events.
>>I would be interested in hearing any comments to this. For a given
concentration of mutagen, the expected number of hits to the genome
would be constant. Therefore, adding "junk" DNA would dilute the number
of hits to coding regions. Furthermore, since the DNA would be organived
in discrete structures (chromosomes), one would expect an increase in
the gradient between the free mutagen and DNA-mutagen complex...
efectively diluting the mutagen locally around the DNA.
PS: Methods in Enzymology (v233) has some neat discussion of radical
attack on DNA and these gradients. I think they could apply equally well
to many mutagens.