Re: Get your New Junk here!

In message <1182091342.408010.53390@xxxxxxxxxxxxxxxxxxxxxxxxxxxx>, Friar Broccoli <EliasRK@xxxxxxxxx> writes
On Jun 15, 10:55 am, "Perplexed in Peoria" <jimmene...@xxxxxxxxxxxxx>
wrote:
"Friar Broccoli" <Elia...@xxxxxxxxx> wrote in messagenews:1181914352.269873.224750@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx

This is just to thank you for giving me a much deserved beating
on my mention of Haldane's dilemma. I seem to have as much
difficulty remembering what it actually says (together with all
the conflicting reinterpretations) as I do remembering the
difference between "its" and "it's". I actually have that one
written on my wall in front of me at eye level. Any more of
this, and I may need to add Haldane to that list.

What I am trying to think about is a kind of meta-evolution
where species are evolving to evolve (by allowing selection to
proceed on more less-harmful mutations) something I "believe"
must be happening, but I keep butting up against all those
annoying facts. I actually have a book on this topic that I
haven't got to yet. Regrettably my ability to acquire and
absorb new information seems to be orders of magnitude lower
than many others in this group.

You might find something useful if you look up the evolution of evolvability.

On the one hand organisms "wish" to reduce the number of detrimental mutations, which means that there is pressure to improve DNA proof-reading and repair, to the point where the cost of the mutations equals the cost of the proofreading and repair mechanisms. On the other hand organisms "wish" to increase the number of beneficial mutations, and in particular "wish" there to be sufficient beneficial mutations to track environmental changes, or keep up in intraspecific or interspecific arms races. It seems to me, although I have not modelled this mathematically, that consequently this will result in a mutation rate a little higher than that would results from the balance of the costs of detrimental mutations and DNA proofreading and repair mechanisms.

If the ratio of detrimental to beneficial mutations differs between mutations affecting protein structure, and mutations affecting gene expression then it would be beneficial to tune the ratio of these two classes of mutation. If say, transposon activity, has a different ratio for these categories from say, point mutations, then increasing the amount of transposon activity (and hence junk DNA) might be beneficial.

However there are other possible explanations for the variation in the amount of junk DNA; there is the relative metabolic cost argument, the cell size argument, the protein domain shuffling argument, and the nearly neutral selection argument PiP mentioned upthread.

--
alias Ernest Major

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