Ken-
Is it surprising to you that measurable
reality is different from “what conventional wisdom says”? I
think the popular notion is firmly entrenched (thanks to all those 50’s
and 60’s atomic horror sci fi movies?) that mutation = BAD, not just
mutation = change. There are fewer examples in the popular culture of a “mutant”
being a force for good than an incarnation of evil. Who even cares about
mutation if it’s silent?
I agree with the notion that the vast
majority of mutations are probably silent, but without a change in morphology
or function it is quite difficult to get people who don’t REALLY believe
in the cellular basis of life (let alone how DNA influences proteins that alter
cell function) to accept that any “change” at all has occurred.
I think that’s why I teach about mutations causing changes that can be
acted on by selection forces. It’s a much more attention-getting
entrance into the subject.
Margaret W.
From:
HAPS-L-owner@xxxxxxxxxxx [mailto:HAPS-L-owner@xxxxxxxxxxx] On Behalf Of Ken Saladin
Sent: Friday, February 23, 2007
5:40 PM
To: HAPS-L@xxxxxxxxxxx
Subject: RE: [HAPS-L] Mutations
We only see noncoding DNA in living organisms, so that skews our view
of how many "harmless" mutations occur. We never get to see the
mutations that result in a failure to produce an observable offspring.
--Bill
William Caldecutt, Ph.D.
Polk Community College
That still doesn't answer my point.
My point is that if 98% of the DNA is noncoding, and IF (an arguable point)
mutations are random with respect to whether they occur in coding or noncoding
regions of the DNA molecule, and IF (also an arguable point) mutations in
noncoding DNA do not harm organismal function, then most mutations can be
expected to be harmless. The fact that lethal mutations are not represented
among the living observable population is quite irrelevant to that prediction.
That second "if" may be the most salient, since damage to noncoding
DNA perhaps can affect spacing or other nontranscriptional functions that might
affect organismal function. But even if the frequency of harmless mutations is
offset by that, it still seems plausible that mutations may be harmless much
more often than the conventional wisdom says -- indeed perhaps in a substantial
majority of cases. Even if some mutations of noncoding DNA did affect spacing
or other structural functions, it would take an awful lot of mutations of that
sort to offset that 98% figure.
Ken