Genetic memory vs natural selection

Pierre sonigo at cochin.inserm.fr
Sat Oct 9 11:11:44 EST 1999


Mike Clark <mrc7 at cam.ac.uk> a écrit dans le message :
ant091128b49Pk=+ at mrc7acorn1.path.cam.ac.uk...
> In article <199910082057.SM00496@[216.1.197.7]>, Jay and Nancy Mone
> <URL:mailto:jaymone at PAONLINE.COM> wrote:
> > Pierre,
> > In all of my years as a biology teacher, I have never heard of the term
> > genetic memory.  What in the world is it?  As long as we are on the
> > subject, exactly what is a non-valid evolutionary history??
> > From a purely evolutionary standpoint, genetic adaptation is a shprt
term
> > phenomenon.  Genetic variability can not anticipate future selective
> > pressures.  Rather, natural selection for any phenotype provides
> > advantages to the cell or organism only in the present environment.  If
> > that environment changes, any particular pre-existing adaptation may or
> > may not remain advantageous.
> >
> > Jay Mone'
> >
>
> This is an interesting question with regard to the immune response. There
> is no doubt that there are certain pathogens, infectious agents and other
> antigens which we are almost certain to meet in our lifetimes. As such it
> may be advantageous to inherit receptors specific for these types of
> antigen if we are able. In that way we are pre-prepared for the almost
> inevitable encounter. There are other antigens of a less predictable
nature
> and for these an adaptive immune response which uses generation of
> diversity at the somatic cell level is advantageous. Many species use both
> strategies ie a balance between a large number of inherited receptors
> each with predefined ligands and an adaptive immune reponse involving
> T-cells, B-cells and immunoglobulin.
>
> I am also supportive of the idea that there is a degree of overlap between
> the inherited receptors of the innate immune response and rearranging
> receptors of the adaptive immune response. By this I mean that some of the
> V-region elements of the adaptive immune response already have a
> preselected affinity for some antigens such that an immune reponse can be
> generated very quickly by B-cells or T-cells with a high clonal frequency.
>
> Examples of this I would cite are the anti-blood group antibodies.
> Virtually everyone makes antibodies specific for the blood group alleles (
> mainly carbohydrate epitopes) that they don't inherit. These antibodies
are
> all encoded by common germline genes within the population which do not
> require extra somatic mutation to enhance their affinity for the sugar
> antigens.
>
> The inheritance of the receptor genes could be argued to be the genetic
> memory of the species.
>
>
> Mike Clark,                        <URL:http://www.path.cam.ac.uk/~mrc7/>
> --
>  o/ \\    //            ||  ,_ o   M.R. Clark, PhD. Division of Immunology
> <\__,\\  //   __o       || /  /\,  Cambridge University, Dept. Pathology
>  ">    ||   _`\<,_    //  \\ \> |  Tennis Court Rd., Cambridge CB2 1QP
>   `    ||  (_)/ (_)  //    \\ \_   Tel.+44 1223 333705  Fax.+44 1223
333875

Interesting point.
Your hypothesis requires that individuals with high affinity antibodies to
blood group molecules had a selective advantage. Some antibodies protect
against the rhesus incompatibility problem during pregnacy. Is it what you
suggest ?





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