What is a gene?

Ron Kagan rkagan at ewald.mbi.ucla.edu
Sat Feb 12 15:50:59 EST 1994


Re: What is a gene?

In article <1994Feb12.181821.927 at galileo.cc.rochester.edu> RICHARD P.
PHIPPS, PHIP at BPHVAX.BIOPHYSICS.ROCHESTER.EDU writes:
>In <CL2F6J.3DF at pnfi.forestry.ca> lmarshal at pnfi.forestry.ca writes:
>
>> In <2jeiua$913 at news.mic.ucla.edu> Ron Kagan
<rkagan at ewald.mbi.ucla.edu> writes:
>> 
>> >How about: 
>> 
>> >	  A gene is a segment of DNA/RNA that, when
>> >transcribed/reverse-transcribed, 
>> >		leads to a biologically functional product.
>> 
>> What about a genic location holding an allelic sequence that
>> produces a protein that is non-functional.  Not a gene anymore?
>> 
>I think that any stretch of DNA/RNA which leads to a RNA/protein product
should
>be referred to as a gene, functional or not (except perhaps for the
occasional
>pseudogene which is transcribed).  I also think that the definition of
the
>physical boundaries of a gene in the statement above should be expanded
to
>include all proximal and distal regulatory regions (promotors,
enhancers, etc)
>involved in the transcription of that gene.  This would not include
soluble
>regulatory molecules - just the appropriate regions of DNA.
>
>Rick Willis 
>University of Rochester Cancer Center


I think that the correct term for any stretch of DNA/RNA which leads to a
RNA/DNA product is *transcription unit*, not gene.  The reason that I
include biological function in my definition of "gene" is that a
definition should include the most essential characteristic(s) of the
entity being defined; that is, the one(s) that best explains all (or
most) of the other characteristics of the entity.

In the case of a gene, even without knowing about transcription or
reverse transcription, we know that genes are units of heredity, are
factors that determine characteristics (phenotype) of an organism,  are
carriers of biological information, and are subject to the forces of
natural selection.   A non-functional transcription product does none of
these.  It is soon lost (in terms of evolutionary time) from the "gene
pool" because there are no selective pressures to maintain it, and it
carries no information.  In this regard, it is like a string of random
letters: "xfrk", which does not constitute a word, even though words are
composed of letters, because it conveys no meaning (information).

Aside from "transcription unit", there is a term for a segment of DNA
that is recognizable as having once encoded a functional product, but no
longer does: "pseudogene".

*It is only because a gene encodes a biological function that make it all
of the things that we know a gene to be: a unit of information, heredity,
and natural selection.*

Therefore, I stick to my original definition:

A gene is a segment of DNA/RNA that, when
transcribed/reverse-transcribed, 
leads to a biologically functional product.


Ron Kagan
rkagan at ewald.mbi.ucla.edu



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