Re: Can genomes sense their population size and adjust their amount of junk DNA accordingly?


"Jim McGinn" <jimmcginn@xxxxxxxxxxxxx> wrote in message news:dos4d8$o52$1@xxxxxxxxxxxxxxxxxxxxxx
>
> "Perplexed in Peoria" <jimmenegay@xxxxxxxxxxxxx> wrote
>
> >> >> > Simply imagine that the amount of junk appearing in a species
> >> >> > results from an equilibrium between the rate of junk generation and
> >> >> > junk removal.
> >> >>
> >> >> Why would we have to imagine this? Isn't this always the case?
> >>
> >> No response.
> >
> > Actually, it is not always (tautologically) the case, at least as I
> > meant it. There are actually three 'forces' involved in creating a
> > balance or equilibrium (assuming that there IS an equilibrium).
> >
> > There is (hypothetically) (1) a molecular-level force of junk generation,
> > (2) a molecular-level force of junk removal, and (3) the force of natural
> > selection which does nothing to the level of junk in any individual, but
> > which by differentially killing or reproducing individuals may result
> > in a change in the level of junk in the population.
>
> That there is any such thing as, "molecular-level force of junk generation"
> or "a molecular-level force of junk removal," seems little more than a wild
> conjecture to me. What is the source of this new found "force" that you are
> conjecturing into existence? Are these real forces distinct from the known
> forces of physics (gravity, magnetism, kinetic movement, etc.)? And natural
> selection is not a force it's a process that has many different forces
> involved.

In common parlance, a process which causes change in a particular direction
is often referred to as a force. There are certainly molecular-level
processes tending in both directions - increasing the amount of 'junk' and
decreasing it. Consult any textbook on molecular biology and search
for keywords like 'intron', 'satelite DNA', 'gene conversion', 'tandem
repeat', or 'pseudogene'.

Here is a link to one online textbook:
http://www.ncbi.nlm.nih.gov/books/bv.fcgi?call=bv.View..ShowTOC&rid=mboc4.TOC&depth=2

> > What I was requesting you to imagine was that (3) natural selection
> > is ineffective, and that the equilibrium arises from a balance between
> > the other two forces. You asked "Isn't this always the case?". The
> > answer is that no, it is not, since your hypothesis is that natural
> > selection is effective and overwhelms the molecular-level forces.
>
> Come on, Perplexed, you constructed this explanation out of two "forces"
> that you just imagined into existence.
>
> >
> >> >> > Also assume that the most effective method of junk removal
> >> >> > is to occasionally remove stuff on one chromosome which seems to be
> >> >> > an
> >> >> > insertion
> >> >> > as compared to the other chromosome.
> >> >>
> >> >> You completely lost me. I haven't the slightest Idea how any of this
> >> >> relates to the discussion at hand.
> >>
> >> No response. (Not a good sign.)
> >
> > Sometimes, as is the case here, my lack of a response can be taken as an
> > indication that I agree with you.
>
> Well, now I'm perplexed. Read what you are agreeing with.

That you are completely lost. That you "haven't the slightest idea".
I completely agree.



.

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