The Nature of Mutations II

Well arguably this is already known to some extent look at the recombination of VDJ in immune cells. But that is a heritable change in that cell line.

Very cool...that simplifies things a bit.

I think there has been some suggestion that similar
deliberate alterations are linked to memory within
the brain ... that being why the membrane surrounding
the brain doesn't allow the immune system cells in.Within a cell-lineage would a deliberately invoked
change constitute a 'mutation'?

Why would you thin VDJ recombination is deliberate?
I would say it does constitute a mutation, however, it is somatic and will not be heritable.

I thought it was related to stuff like:
http://www.midwconfimmunol.org/...ter98/posters/winstead.htm...and that made me think there was some mechanism involved
in the gene conversion.I agree that immune response is somatic and so non-heritable,
but it's the possibility of such mechanisms that made me
include 'unpredicted' in a broad brush 'mutation' definition.

Think of it as the recombination provides the novel variation with pathogens acting as the selective pressure...your immune system does not a priori know what pathogens you will encounter so a mechanism has evolved to make it highly variable (somatically) to give it a chance to recognize and combat the pathogens you will encounter in your lifetime...the mutations are random but also so much variation is developed there is a chance that some combination will recognize almost any pathogen you will encounter...it is also an arms race as the pathogens will have to evolve a way of avoiding your immune system.

I thought it was something that happened in response
to pathogens.

The selection of a specific recombinant, expansion of the T cells with that recombinant happen in response to the pathogen...but VDJ recombination/mutation occurs regardless of challenge or not...like I said, the immune system cannot anticipate the challenge.

Ok.I still feel that mutation has to include a concept of
'unpredicted' as well as 'change' though.

I am not sure what you ar getting at...the only thing I object to is any pre-adaptational association of mutation i.e. what Peter Borger advocated in mutations were pre-determined so that instead of selection the organism pre-adapted to an environment that it somehow know was coming rather than what has actually been observed which is there is variation and the environment exerts selective pressure for or against a particular variant(s).[This message has been edited by Mammuthus, 07-17-2003]

I suggested that a broad defintion of mutation
was simply an 'unpredicted change' between parent and
offspring ... WoundedK then asked why I included 'unpredicted'
and I said 'Well, in case there are any mechanisms that make
changes' ... and WK said 'VDJ...' I (mistakenly I think) thought
that this was a change in response to a stimulus, and so could not
be considered a 'mutation' in my view.And we get about here.Interestingly the way I look at it, Peter Borger's 'non-random
mutations' wouldn't actually be mutations anyhow (even if they
existed in the first place).PS: This is getting like a chat room today!!!!

Arguably it is in response to stimuli, the stimuli just happen to be the developmental signals that have fated the cell to be that particular part of the immune system such as the interleukins.

If it's a response to a stimulus it's not a mutation
it's a direct adaptation.

Only by your new arbitrary criteria. Are the mutations cause by mutagenic chemicals for genetic screens somehow not mutations because they are caused by an environmental factor. Is the knocklout mouse I produce transgenically not also mutant just because it was produced artificially?Why this emphasis on the origin of the change?

Mutagens don't stimulate a specific change, they increase the
probablity of some 'copy error' taking place.Similarly deliberatley knocking out a gene is not a mutation,
it's a targetted act.The origin of the change is a fundamental feature of the
nature of mutations, surely. You cannot state what a mutation
is without reference to ... well, what a mutation is.