DNA Question

Richard Gordon gordonr at cc.UManitoba.CA
Thu Dec 17 07:22:37 EST 1998


>On Wed, 9 Dec 1998 16:31:06, "Dr. Peter Gegenheimer"
><PGegen at UKans.nolospamare.edu>, re: comments by John McKechnie
><J.M.McKechnie at ncl.ac.uk> wrote (in
>part):
>What about the opposite scenario, the one you propose? Is it possible for
>there to
>exist a string of binary digits which corresponds to valid, executable
>instructions
>for two different microprocessors? I think it possible but not plausible,
>because of
>the conflicting constraints placed upon the code. As you point out, this
>might be
>resolved by altering the hardware. Ultimately, this seems like a question for
>theoretical mathematics: I bet one could prove that it is possible or
>impossible to
>design such a bifunctional code.

Dear Peter & John,
Two cases of dual functioning of the same DNA come to mind:

a) the same sequence is read twice, with a frame shift;
b) the same sequence is read in both directions, on opposite strands.

Of course, I'm interpreting "same" a little more liberally than the intent
of the original question, but all the constraints notwithstanding, dual
functioning does occasionally occur.

Many embryos have alternative morphologically distinct states at
intermediate stages. This can even occur in the same species, even in the
same batch of eggs, and seems to correlate with egg mass. It is usally
noted as alternative modes of gastrulation. Of course, the DNA is
essentially identical between these varying embryos, and in a sense is thus
"dual functioning". If Donald Williamson* is correct that some
metamorphosing organisms have two genomes that are concatenated into one,
then their DNA is again dual functioning. The same might be true of
organisms with morphologically identical haplontic/diplontic life cycles,
and organisms related by a change in ploidy.
Yours, -Dick Gordon
*Williamson, D. I. (1992). Larvae and Evolution: Toward a New Zoology. New
York: Chapman & Hall.
Dr. Richard Gordon, Department of Radiology
University of Manitoba, Health Sciences Centre
820 Sherbrook Street, Winnipeg, MB R3A 1R9 Canada
Phone: (204) 789-3828,  Fax: (204) 787-2080,  E-mail: GordonR at cc.UManitoba.ca
The Hierarchical Genome: http://www.wspc.com.sg/books/lifesci/2755.html




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