Re: [asa] Two questions...Ayala's article

>Hi Preston,
>
>I *think* the answer is that a shorted track on a circuit board is a
>poor analogy to an error in DNA.
>
>The better analogy would be;
>
>An error in DNA = error in the coding of the machine making the circuit board
>
>An error on the circuit board (eg. shorted track) = an error in
>brain "micro structure"
>
>In other words; having a bad track on a PCB is a "minor" flaw (as
>would be loosing a connection between two neurons in the brain)
>whereas an error in the production process would be "major" (as
>would a DNA flaw leading to disfunction in entire areas of the
>brain).
>
>Or, at least, so it seems to me.
>
>Blessings,
>Murray
>

I'm not disagreeing that speech probably goes back a long way. I'm
just saying that the fact that one mutation can knock it out is not
an argument for or against that. There are countless single mutations
that can knock out a major function - look at Online Mendelian
Inheritance in Man on the web for the current catalog. Those are just
the ones that leave development intact enough for an inherited
disease to be recognized.

Just the fact that a system is major and complicated doesn't mean
that it has to be robust to mutations. Memory chips and processors
may be designed to be that way, but biological systems aren't.

If the point is that a major system of genes must be so finely tuned
that it can't be modified at all without messing up development, it's
just not true. There are many polymorphisms known in individual
downstream elements (enzymes and other proteins) of these systems
that have functional consequences without causing catastrophic
failure of development.

More to the point, there are polymorphisms in high level regulatory
genes, both in coding regions and regulatory regions, that result in
substantial functional differences that result from changes in the
expression level of many proteins. There are instances of differences
in personality, a propensity to anger, for instance, that are caused
by variants that are out there in the population at substantial
levels. The fact the they are there at significant frequencies means
that they are perfectly compatible with development and not selected
against very strongly.

Is this to the point at all?

Preston

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Received on Wed Feb 25 20:48:59 2009