From: Robert J. Bradbury (bradbury@aeiveos.com)
Date: Fri Jan 10 2003 - 11:33:49 MST
On Fri, 10 Jan 2003, Nathanael Allison wrote:
> I always thought the junk DNA was just there to speed up mutation.
Not to "speed up" mutation, but as a side effect of transposons
that do function to speed up mutation. It's the "waste" left
over after you finish cutting a pattern out of the cloth.
> The presense of more DNA would speed up the rate of mutation.
No, rates of mutation are reasonably stable -- organisms, particularly
lower organisms with short life cycles, can vary them to match the
environmental conditions (harsh environment... current program isn't
working... increase mutation rate to get a better program...). This
is a "real" phenomena, its called the "SOS response".
> Also it might have some effect on recombination of chromosomes, crossing over.
Evidence for this has only recently come to light. I've seen at least
one reference that suggests that the junk DNA may play a role in chromosome
alignment for recombination purposes. But there *are* organisms, e.g.
Fugu, with very little junk DNA so this function isn't "essential" for life
or evolution.
> It might even have messages to sabatogue the DNA in some sense to create
> more mutations or other changes.
The primary purpose of transposons is the entire "selfish-gene" hypothesis --
i.e. to make copies of themselves. *But* in so doing they also seem to
make copies of other "useful" genes. That allows organisms to keep one
copy of a gene doing its old function while evolving a new copy of a
gene to do something novel (and potentially useful from an evoluationary
standpoint).
> Either way just by exsisting whether it does anything or not
> speeds up evolution. Any thoughts?
Transposons (which are the source of junk DNA) do speed up evolution.
However, there may be a secondary use for junk DNA which is to
function as a "free radical/toxin sink". This is very unclear at
this point since one may have organisms with similar lifespans
with very different amounts of junk DNA (so the extent to which
this strategy is used is very unclear). But it does make logical
sense -- if an organism is consuming X amount of toxins or generating
Y amount of free radicals due to metabolic activity then it would
be much better if those agents were damaging "junk" DNA than "useful"
DNA. It is, to my knowledge, a poorly studied area of biology.
Robert
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