Received: by alpheratz.cpm.aca.mmu.ac.uk id WAA08761 (8.6.9/5.3[ref pg@gmsl.co.uk] for cpm.aca.mmu.ac.uk from fmb-majordomo@mmu.ac.uk); Sun, 11 Feb 2001 22:40:17 GMT From: <Zylogy@aol.com> Message-ID: <a6.fdc4cda.27b86e2d@aol.com> Date: Sun, 11 Feb 2001 17:37:33 EST Subject: Re: Less genes than expected To: memetics@mmu.ac.uk CC: Zylogy@aol.com Content-Type: multipart/alternative; boundary="part1_a6.fdc4cda.27b86e2d_boundary" Content-Disposition: Inline X-Mailer: 6.0 sub 10506 Sender: fmb-majordomo@mmu.ac.uk Precedence: bulk Reply-To: memetics@mmu.ac.uk
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It doesn't really matter that vertebrate genomes have "fewer" "fixed" genetic
sequences than one might expect on the basis of average size of a gene versus
the overall size of the genome carrying them. Because of variable editorial
capabilities on transcription RNA, the "true" number of final protein
products is vastly greater. Many people are under the impression that the
genome, like the lexicon, is simply some vast repository of fossil forms.
Sure, they allow for duplication and mutational modification leading to
variants of the "same" gene, but that's about it. In reality, though, the
genome itself is in constant, if glacially slow, flux. Introns and exons
shuffling about, not to mention the repetitive intervening sequences (the
so-called "junk" DNA) which regulate accessibility and activity of genes in a
physicomechanical fashion. And because of viral incorporation and accidents
of recombination, stuff is coming into the genome in unexpected places from
outside. And sometimes genetic sequences are simply lost, or permanently
inactivated.
Despite all this, its a very sophisticated production system. And when
considering its origins, one must see that it has been assembled throughout
the history of life. Indeed, in eucaryotic cells many organelles show
evidence of genetic independence at one time, but now most of the genes have
either been transferred to the main nuclear genome or products of functional
equivalents from there replace the originals in the organelle. Flux.
In addition, many of the very complicated genes appear to have been welded
together from standard, smaller parts (just as in language). One wonders how
much of this still goes on.
So in the end, what really is the true "number" of genes? Do we count all the
variants of a single thread as separate units (such as hemoglobins) or one.
Where would THAT end when many different functional types can be shown to
have evolved from a single type (proteases, for instance)? Or do we take the
easy way out and simply count the number of sequences able to be transcribed
into RNA (and then protein)?
I think this is still an open question, and one subject to debate.
Jess Tauber
zylogy@aol.com
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