Text 1063, 97 rader
Skriven 2004-12-17 21:43:00 av Rich (1:278/230)
Ärende: Re: Article: The evolutio
=================================


This is very interesting stuff.  It seems to me that ontogenesis
probably is controlled by a genetic machine that sequentially
expresses a lattice of the "mosaics" mentioned in the article,
so the whole embryonic development sequence could be
described in the genome also, as a structure to be interpreted
during ontogeny.

Rich




Robert Karl Stonjek wrote:
> Evolutionary genetics: The evolution of evolution
>
> G Bell*
>
> *Biology Department, McGill University, 1205 ave Docteur Penfield, 
> Montreal,
> Quebec, Canada H3A 1B1
> Correspondence to: G Bell, e-mail: Graham.bell@mcgill.ca
>
> Heredity (2005) 94, 1-2. doi:10.1038/sj.hdy.6800608
> Published online 3 November 2004
>
> A recent claim, that the ability of genetic systems to evolve will itself
> evolve in a predictable fashion, brings a new challenge to our studies of
> evolution. It is commonly accepted that environmental change leads to
> adaptation through natural selection, within the constraints set by a
> particular genetic system. It is much less straightforward to enquire
> whether a genetic system itself can evolve, and, if so, what the
> consequences would be. Earl and Deem (2004) have recently claimed just 
> this:
> that a fundamental feature of genetic systems - their 'evolvability' - 
> will
> itself evolve predictably in response to environmental perturbation.
>
> At a low level of genetic organization, this is a familiar phenomenon 
> whose
> mechanism is well understood. In asexual populations, severe environmental
> stress creates intense selection that causes an increase of fitness in the
> new conditions of growth relative to the ancestor. An indirect effect of
> intense selection is the occasional fixation of mutator genes, which 
> usually
> encode defective versions of DNA polymerases, and thereby elevate rates of
> point mutation by factors of 10-1000. They spread, despite the fact that
> almost all the mutations they cause are deleterious, because the mutator
> gene is completely linked to all the mutations it causes. Among the large
> number of mutations that the mutator causes will occasionally occur a
> mutation that confers increased fitness in the new environment; as this
> beneficial mutation spreads through the population, it will carry the
> mutator with it. Conventional population genetics theory can describe this
> process and it has also been demonstrated in the laboratory (eg Sniegowski
> et al, 1997).
>
> It is now clear, however, that evolutionary change does not always proceed
> smoothly through base substitution at single loci. The mosaic nature of
> bacterial genomes, the mobility of plasmids and other genetic elements, 
> the
> idiosyncratic nature of mating-type genes in sexual microbes and the 
> genetic
> regulation of development in multicellular organisms all show that 
> variation
> at higher levels of genetic organization is also important in evolution.
> (For a set of papers describing such phenomena, see Genetica, Vol 118,
> 2003). Such higher-level sources of variation are hard to incorporate in
> theoretical evolutionary modelling, which usually relies on defining a
> restricted range of genotypes and then finding out which remain after
> selection. Individual-based computer simulation is one promising 
> alternative
> to the standard approach. In this alternative approach, types or
> combinations of types with unexpected properties may appear and spread
> during the course of the simulation. Systems of this sort are now being 
> used
> to investigate the fundamental features of evolutionary change that are
> inaccessible to equation-driven methods (eg Yedid and Bell, 2002; Lenski 
> et
> al, 2003).
>
> Full Text at Nature Heredity
>
http://www.nature.com/cgi-taf/DynaPage.taf?file=/hdy/journal/v94/n1/full/6800608a.html

>
> Posted by
> Robert Karl Stonjek
>
>
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