junk DNA

Ian A. York iayork at panix.com
Tue Apr 18 07:37:55 EST 2000


In article <20000418002618.12411.00000938 at ng-ck1.aol.com>,
Rcjohnsen <rcjohnsen at aol.com> wrote:
>
>   I have over 20 pages of abstracts on alu sequences.  If they are not
>important then why do they comprise such a large amount of our DNA?  Just along
>for the ride?  That may be your conclusion, but I think it premature and  still
>an open question.

If herpes simplex virus isn't an important and functional part of our
genome, why is it such a large proportion of our neuronal DNA? If rust
isn't an important and functional part of my car, how come there's so much
of it?

You're arguing from a false assumption: that everything in the genome
*must* be functional.  The original question is, *is* junk DNA
functional?  You can't answer a question by assuming the answer.

The one thing we know about alu elements is that they can replicate
themselves, and their involvement in genetic disorders suggests that they
do so randomly.  Simply based on that, you'd expect it to be abundant.  
(Thoguh don't overestimate it.  Alu elements are a tiny fraction of the
genome.) 

In essense, alu elements are stripped-down viruses.  You don't expect
herpes simplex or spumaviruses to be selected for--they're just there,
parasitic pieces of DNA that are along for the ride.  Same goes for alu
sequences.

Ian
-- 
    Ian York   (iayork at panix.com)  <http://www.panix.com/~iayork/>
    "-but as he was a York, I am rather inclined to suppose him a
     very respectable Man." -Jane Austen, The History of England




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