On 4 Nov 1998, Donald Forsdyke wrote:
> But surely, as soon as a piece of DNA "thinks" of encoding a protein,
> selection becomes operative on the protein. Can there really be a period
> prior to selection kicking in?
Ok, can we stop being pedantic now and help this person express
his idea? Of course it is a mistake to say that non-coding DNA
represents DNA "before" selection, and coding DNA represents DNA "after"
it. Nevertheless, we can make a comparison of amount of variation
or rates of evolution between coding and non-coding, and this
will tell us something about the influence of selection relating
to specifically to coding. This is an obvious method that is
used repeatedly by professionals in experimental population
genetics.
> What you seem to be missing out is that selection may have acted on
> the piece of DNA before it "thinks" of becoming a protein-encoding gene,
> (and even after it becomes a protein-encoding gene selection may be
> acting on it for genomic reasons discussed elsewhere:
Yes, and if these are truly "genomic" factors, they will
constitute a "background" set of conditions that applies to
coding and non-coding DNA, and will be factored out in the
coding-vs-non-coding comparison, so that your point is moot.
Arlin
Arlin Stoltzfus, Ph.D.
email arlin at carb.nist.gov; phone 902 494-2968; fax 902 494-1355
mailing addresses:
current: Biochemistry, Dalhousie U., Halifax, NS, B3H 4H7 Canada
near-future: CARB, 9600 Gudelsky Drive, Rockville, MD, 20850 USA
