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Anyone Seen Evolution?

Greg Ad cock gjadcock at cheops.anu.edu.au
Sun Nov 24 13:34:10 EST 1996


I think I should add a comment on all this since it was me that mentioned
the insecticide example in the first place. I havn't been following the
thread so this might be a little astray from the main thread.

> In article <sg32-ya023080002111961715360001 at newsstand.cit.cornell.edu>,
> sg32 at cornell.edu (Susan Glueck) wrote:
> 
> > In article <57270p$t73 at scotsman.ed.ac.uk>, rhi at tattoo.ed.ac.uk (Rhiannon
> > Macfie) wrote:
> > 
> > 
> > > > Sounds like natural selection, can you expound on that.  How do I know 
> > > >  there weren't a small percent of insects that were resistant to 
> > > > the insecticide to begin with. 
> >  
> > > But where did this small percent come from in the first place?
> > 
> > Many insecticide resistance mutations involve a minor (minor in the sense
> > of requiring only a small point mutation) alteration in amino acid sequence
> > of a particular receptor protein which renders the particular pesticide
> > ineffective. 
> 
> 
> Please be aware that mutation is not evolution.  Mutation provides the
> ultimate raw material upon which natural selection can act.
> 
> __Evolution requires both natural selection and genetic variation.__

This last bit I have to agree with although I would add "stochastic
processes" to the last sentence. 

Where did the smallpercent come from in the first place? This is where
laboratories are wonderful things. With a uniform genetic population of
Drosophila (or Musca or Lucilia or Aedes or the pest of your choice) that
can be shown to be 100% sensitive to insecticide one can apply mutagens
and get flies resistant to the same dose. This is not all though. Almost
every time this is done, the genes that are found are the same ones as are
found in the field (well they map to the same location on the genome)...
and no, field strains have not infected the lab stocks. Various groups
have looked at the DNA changes in field and lab selected resistance
alleles and found identical mutations.

I should add that, in Australia at least, undergraduate lab classes often
include a selection experiment of some sort using bacteria. 

Greg



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