Re: Molecular Evolution
From: Jason (falciparum_at_hotmail.com)
Date: 01/27/05
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Date: Wed, 26 Jan 2005 23:50:39 -0500 (EST)
Perplexed in Peoria wrote:
> "Jason" <falciparum@hotmail.com> wrote in message
news:ct8h7c$2r4k$1@darwin.ediacara.org...
> > I was wondering about a gene duplication event in which the new
gene
> > causes a 2X dosage that has a negative effect on the organism (say
> > before the duplication this gene was under selective constraint).
>
> By "under selective constraint" do you mean the same as saying
> that the gene product is a "constituitive enzyme"?
No. Selective constraint means that mutations resulting in an amino
acid substitution (non- synonymous) will likely be eliminated by
natural selection. This is in contrast to genes under positive
selection, for example an antigen, in which non-synonymous mutations
are actually "preferred." The point of assuming the duplicated gene in
my question is under selective constraint is so that once another
redundant copy is there making the same protein, the selective
constraint can change.
> > After the duplication it seems to me that both redundant genes
might be
> > under positive selection
>
> Did you mean negative selection?
No. Positive selection (i.e., changes being "better") would be
preferred in this situation because the 2X dose from the gene
duplication would make substitutions in these genes a good thing.
> > until one loses function, or both lose some
> > portion of their function. Might this result in genes with mostly
> > purifying selection regions, but some positive selection regions?
>
> I don't know what you mean by a "selection region", nor what it
> might mean for a selection region to be "purifying" or "positive".
I mean a region of the gene. Different parts of the same gene can be
under different selective pressure. Purifying selection is like saying
"selective constraint."
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