Genetic memory vs natural selection
mrc7 at cam.ac.uk
Sat Oct 9 06:04:28 EST 1999
In article <199910082057.SM00496@[18.104.22.168]>, Jay and Nancy Mone
<URL:mailto:jaymone at PAONLINE.COM> wrote:
> 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
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
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