Re: microreversibilty of a mutation

On Wed, 25 Jul 2007 12:16:59 GMT, Ye Old One <usenet@xxxxxxxxx> wrote:

On Wed, 25 Jul 2007 08:36:15 -0000, "vent.du.sud@xxxxxxxxx"
<vent.du.sud@xxxxxxxxx> enriched this group when s/he wrote:


Hi there,

I am working on modeling the spread of mutations and wonder about one
common assumption which is always made: the microreversibility of a
mutation. If a mutation from A to B has a probability p(A->B) then the
reverse mutation has the same probability p(B->A)=p(A->B).
One direct consequence of this hypothesis is that if evolution is
driven by external conditions it is however possible by inverting
these external conditions to revert the evolution (forget the DNA
mixing).
Now from a thermo statistical point of view one expects the
transition probability to be Boltzmann like:

p(A->B)=Cte*exp(-Eab/T)

Where Eab is the energy gap between the two states.

Such a probability breaks down the micro reversibility and inverting
the external conditions does not necessarily bring back B to A. So my
question is twofold:

Is there any hard proof of p(A->B)=p(B->A) ?
If so is there an explanation why is not the Boltzmann transition
probability which has to be used ?

Note: If p(B->A) is non equal to p(A->B) then one has to reconsider
all the works which has been done on the timing of evolution.

Reverse mutation, in effect the repair of one gene by the actions (or
inactions) of others, happens all the time.

South wind-- This repair works through an entirely different
mechanism than the original mutation and therefore there is no
relation between the two probabilities.

You should also know that microreversibility does not even begin to
suggest that the evolutionary process is reversible. You might as
well argue that diffusion is reversible even though every aspect of
molecular collision involved is reversible.

Or think of this model: lay out a deck of cards on a table, each card
face down. Now randomly start turning over cards, whether face up or
face down. Are you ever going to return to the original all-down
condition? Essentially no (the probability is too small to consider).
This, even though each card flip is completely reversible.

.

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