Re: Is there any reason for the evolution to be one way
- From: "Shaktyai" <Fabrice.Allais@xxxxxxxxx>
- Date: Tue, 27 Mar 2007 00:01:16 -0500 (EST)
On Mar 26, 7:17 am, drosen0...@xxxxxxxxx wrote:
Let's crunch some numbers: Has anyone ever calculated the energy
required for the mutations A - >B, and B->A . Has anyone ever
compared the stress along the segment of a DNA before and after a
mutation ? If they are equals then p(A)=p(B). If they are different
then p(A) non equals p(B). It is that simple.
Although I haven't done the calculation needed, I can get some
idea of what is going on by looking at the nature of some important
mutations.
1) Fusion of two chromosomes
2) Breaking up of one chromosome.
According to some recent studies, these are two mutations
common in the evolution of man and other organisms. The conformational
change in the chromosome are obviously small compared to the energy of
putting the chromosome together in the first place. The stresses
aren't going to change very much, since we are talking about loose
strands here. Whether the chromosome is terminated or not doesn't
affect the nucleotides a few units from the ends.
If you look at the DNA from a physicochemist point of view then
mutations are just chemical reactions that lowers the local free
energy.
No, the mutation can raise the local free energy. There is
absolutely no constraint on the local free energy going up. If there
are only two choices, then the mutation is almost exactly reversable.
The probability of a mutation occurring with the energy going down a
small bit is almost exactly the same as probability of the mutation
occurring in the opposite direction. Think about the Robertson fusion.
Okay, sometime back in time two chromosomes in an ape like ancestor
fused at a nucleotide site. None of the other nucleotides were
directly affected. Given two choices, the probability of a chromosome
splitting mutation is almost the same in terms of free energy.
Thank you for your time and comments. They are always illuminating
though
I disagree with some points. There is plenty of evidence that long
polymer (Flory's work) can be treated with a thermodymical approach.
A Bolztmann probability factor then gives:
p(A->B)=C exp(-E(AB)/kT.
Which is of course non symmetric. Complete or local thermodynamical
equilibrium always favors a local energy minima. One can argue there
is equiprobability for athermic reaction, but one then must explain
why there is a non zero mean deviation (evolution !!!).Of course I
only consider organisms without DNA mixing and cross over. These two
effects are in my opinion the real source of randomness and evolution,
and one of the most beautifull aspect of life.
.
- References:
- Is there any reason for the evolution to be one way
- From: Shaktyai
- Is there any reason for the evolution to be one way
- Prev by Date: Re: Is there any reason for the evolution to be one way
- Next by Date: Re: Is there any reason for the evolution to be one way
- Previous by thread: Re: Is there any reason for the evolution to be one way
- Next by thread: Re: Is there any reason for the evolution to be one way
- Index(es):
Relevant Pages
|
