Tim writes:

>> The sentence you quoted, "The extensive use of gene conversion appears 
>> to play a role in the ability of the Y chromosome to edit out genetic 
>> mistakes and maintain the integrity of the relatively few genes it 
>> carries," is fundamentally in error.
>
>No - it's fine.  The ability to produce genomes with zero mutations out
>of genomes with one or more mutation is what is needed to overcome
>Muller's ratchet - and that's /exactly/ what this process provides.
>
>It matters not that it operates stochastically - and will sometimes
>increase - rather than decrease the number of mututions.
>
>The important thing is that it increases the variance in the number
>of mutations.
>
>By doing so it concentrates the mutations in a few individuals - which
>can then be culled by selection.
>
>In terms of repairing errors in your genes, this is a much better 
>scenario than giving all your offspring the same error.

That's certainly the oddest definition of "error repair" I've
ever heard. In
effect, the same could be said for any mutation. Eventually, any point mutation
will "correct" itself by simple random chance. 

Of course, two things accrue to such a strategy: the first is that while you're
waiting for that specific backmutation, the rest of the world will go to hell
in a handbasket. Tthe second is that you're potentially losing a great number
of phenotypes during the mutation's lifetime in the population due to either
inviability or noncompetitiveness. It is the amelioration of this second effect
which is the primary drving force underlying the evolution of error-correcting
mechanisms. Such phenotypic losses significantly render the species as a whole
non-competitive in the sense that the species has now become non-efficient in
maximally exploiting its environment (i.e., producing the greatest number of
successful progeny at the least possible cost). Holding and dominating a niche
is "getting there fustest with the mostest" at the least possible cost.

Randomly implemented mismatch repair does offer the possibility of dramatically
accelerating the time to "correction" for some fraction of the
population, but
it does nothing to minimize the loss of phenotypes to the species. Perhaps if
anything, it locks in the non-competitiveness of a particular lineage in a
manner that can't be easily recovered.

Wirt Atmar
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