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Is "Junk" DNA Used to Provide Genetic Memory

Warren Gallin wgallin at gpu.srv.ualberta.ca
Sat May 7 11:20:28 EST 1994

In Article <graulCpF73w.D11 at netcom.com>, graul at netcom.com (Rick Graul) wrote:
>fiddick at lifesci.lscf.ucsb.edu (Laurence Fiddick;x2791) writes:
>>In <graulCoz9Hq.ILx at netcom.com> graul at netcom.com (Rick Graul) writes:
>>>The purpose of "junk" DNA,
>>>as I understand it, is to provide a reservoir of elements
>>>which can be used by the organism for creating new genes.
>>i'd be interested in any references you might have on the purpose of junk dna.
>>presumably there is some cost to carrying junk dna, and i somehow find it
>>hard to believe that natural selection can maintain it for such uncertain 
>>long term interests--so any refs on this or any other arguments for the 
>>adaptive value of junk dna would be appreciated.
>Here's the medline entry for the paper where I first saw this idea.

>1. Brosius J; Gould SJ.
>     On "genomenclature": a comprehensive (and respectful) taxonomy for
>     pseudogenes and other "junk DNA".
>   Proceedings of the National Academy of Sciences of the United States of
>   America, 1992 Nov 15, 89(22):10706-10.
>     (UI:  93066312)
>         (PE title:  Proceedings of the National Academy of Sciences of the
>         United States of America.)

1) I think saying that the "function" of junk DNA is to hang around and
supply a reservoir of sequence for future unspecified use is fundamentally
unsound.  Natural selection does not work on spec.  If there is no current
selection pressure, then there will be no reason to maintain a specific gene
(Note that is different from saying that if there is no selection pressure
then a gene will necessarily disappear).  Although new genes may be
constructed from the junk, that can not be called a function until it happens.

2) As for that PNAS paper, time will tell but I suspect most people working
the field are not going to take on this weird and not particularly useful
formulation.  I'm surprised that Gould would consider this as a function,
although the abstract seems to say so.  That's like saying humans should
develop gills because someday we may need to become aquatic.

3) Just because it's there doesn't mean that it has a function.  On the
other hand, just because we can't think of a function doesn't mean that it
doesn't have a function.  On the other hand again, its function may be
something other than we think.  How's that for even-handedness.

Warren Gallin,
Department of Zoology, University of Alberta
wgallin at gpu.srv.ualberta.ca

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