DNA Question

Guy Hoelzer hoelzer at med.unr.edu
Wed Dec 9 16:48:35 EST 1998


In article <74m8ka$m1r at net.bio.net>, John McKechnie
<J.M.McKechnie at ncl.ac.uk> wrote:

>For evolution this implies that variation occurs through changes in the way
>DNA interacts with its context, rather than purely through changes in DNA.
>The DNA could be changing considerably in order to keep its interaction with
>its context the same (and thus keep the phenotype the same).

What might cause the interaction to change if neither the DNA or the
environment change?  If you are saying that phenotypic change can be
driven by environmental change without genetic change, I agree.  However,
environmentally induced phenotypic changes are generally not considered
evolutionary, in part because they are easily reversed.  For example, body
size can often be influenced by temperature (or feeding rate) during
development.  Therefore, climatic cycles can produce cyclic increases and
decreases in mean body size.  I am essentially emphasizing the
unpredictable nature of environmental heredity.  Heritability of
environmental conditions does not follow predictable rules like those
governing heritability of DNA variation, and heritable variation is a
basic prerequisite for biological evolution.  Personally, I would say that
the organism is not evolving in the scenario presented above because the
inherent phenotypic tendencies of the organism have not changed.  A small
individual who developed under hot conditions had the potential to be
larger if reared under colder conditions, so the fundamental organism
(independent of its realized phenotype) never changed.

-- 
Guy A. Hoelzer                 phone:  702-784-4860
Department of Biology          fax:  702-784-1302
University of Nevada Reno      email:  hoelzer at med.unr.edu
Reno, NV  89557




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