From: Nigel Hammersted (nigelhammersted@yahoo.com)
Date: Mon Jul 03 2000 - 23:58:04 MDT
--- Damien Broderick
<d.broderick@english.unimelb.edu.au> wrote:
> More to point, I suspect, is that the `rigid coding'
> just sets the
> machinery in motion. Much of development is
> stochastic and/or
> selected/darwinnowed by exploratory activity within
> the local environment,
> especially in the immune system and the brain's
> neural organisation.
this is true with respect to the development of the
phenotype at the macro level, yes; for example, a
mutation occurring early in the development of a maize
plant and giving rise to resistance to the Aspergillus
fungus but simultaneously resulting in fewer viable
seeds would cause only grief to its bearer except
during seasons of unusually dry weather. this is due
to the fact that Aspergillus fungus thrives under
dry-weather conditions. this is "darwinism" at work in
a stochasic environment.
>I don't think transposons leap about inside the
>differentiated cells of
>phenotypes, but rather during the formation of new
>germline cells -
>which
>case one `tight logical program' would be replaced by
>a minor variant.
at the molecular level, changes do regularly occur
within cell lines throughout the lifetime of an
organism. although the greatest amount of research has
been conducted using bacteria, maize has also been
studied, and transposition can take place in somatic
cells as well as germ cells.
the mechanism by which transposition takes place is
not well understood, but it does not appear always to
occur randomly. transposition can be inhibited under
certain physiological conditions such as DNA
methylation. thus, a host can "permit" transpostion or
not.
one of the primary methods of detecting the presence
of transposons is to look for changes in how the
genetic line interacts with its environment. such
changes in bacteria would include a newly acquired
resistance to drugs, indicating that transposons
expedite the evolutionary process.
as to whether transposition is rightly thought of as
operating under a system of "rigid coding," no doubt
the process is subject to the same constraints as any
other sereies of chemical reactions. there are rules;
however, the sequence of events seems to more closely
resemble jazz than symphonic music.
nigel hammersted
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