[Taxacom] biased gene conversion

Kenneth Kinman kennethkinman at webtv.net
Wed Feb 11 14:36:18 CST 2009

Dear All, 
       I find it a little hard to swallow that "many of
the genetic changes leading to human-specific characters may be the
result of the fixation of harmful mutations," and that this contrasts
with "the traditional Darwinistic view that they are the result of
natural selection in favour of adaptive mutations." 
       Although biased gene conversion could accelerate
some evolutionary change (pushing more grist through the mill), natural
selection (the mill itself) is still going to eventually act on that
change. Framing this as an either/or question just seems too simplistic.
A sickle-cell gene is adaptive if you have just one copy, but it is
maladaptive is you have two copies. If a gene is totally maladaptive,
natural selection will weed it out. 
       On a larger time scale, genes making dinosaurs
bigger and bigger was adaptive for many of them during the Mesozoic, but
it was maladaptive when the end-Cretaceous event collapsed their food
supply (as well as being too big to burrow and go into torpor).  
Natural selection keeps on "selecting" no matter how the genetic
variation arises or what environmental changes occur. Frankly, I don't
think Darwin would have any problem with biased gene conversion.
However, I think he might take issue with the premature speculation on
what biased gene conversion might be correlated with (such as
homeothermy).  And there are obviously forces which counteract biased
gene conversion (and I believe that I read that many primate genomes
have actually become less GC-rich compared to some other mammal groups).
A genome is going to eventually start losing information if it doesn't
have enough A-T pairs.  There have got to be some complex trade-offs
that we simply don't understand yet.

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