Frequency/distribution of nucleotides/amino acids before selection

Dr.Ram Samudrala ram.samudrala at stanford.nojunkemail
Mon Nov 2 21:44:42 EST 1998


Donald Forsdyke <forsdyke at post.queensu.ca> wrote:

> Drs. Hickey and Lobry have both accepted Dr. Samudrala's premise
>that base composition changes "before selection kicks in".

The premise is that the amino acid composition is different in a gene
prior to selection (i.e., before selective pressures arise for the
protein encoded by the gene) and after selection [*].  I believe this
follows from the Neodarwinian theory of evolution.  If the
compositions are identical what purpose would selection serve (I do
think that proteins in general are fairly well-clustered around their
average amino acid compositions)?

>How do we know when "selection" first "kicks in"? 

That's related to my question. You can argue selection cannot be
present in a gene that isn't functional.  But I think it is a
difficult question to answer, which is why I asked.

I thank Drs. Hickey and Lobry for their papers which I will look up.

--Ram

* - The data for the latter is present in many text books.


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 God is a conjecture; but I desire that your conjectures should not reach 
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 to me of any gods.  But you could well create the overman. ---Nietzsche




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