I've heard that line of arguments too, mostly from those who've been
reading Lee Spetner's stuff. Is that your source?
>When Tim said "They're out there" what I'd like is where exactly they are.
>I don't want to sound like a jerk, but I really like having things backed
>up with examples. A theory can be great, but w/o actual examples to support
>it, there is no logical support for it, as has been discussed here earlier.
Oh, no problem. Basically, I'd suggest that you first go through MEDLINE
(as I'll describe below) read some abstracts, and become familiar with
idea that there are actually a great abundance of related genes and gene
families in the genomes of organisms. When one sees the variety of possible
forms and the sheer amount of interrelatedness between many genes, one
may develop an better feel for the roles of duplication in evolution.
With regard to duplications, I previously wrote:
T: An increase in the number of copies of a gene can produce an increase
T: in the expression of a gene product (perhaps a useful antifreeze
T: protein?). There are any number of situations where a simple increase in
T: a gene's expression might be beneficial in a particular environment (eg.
T: Growth on a substrate for which some catabolic step is rate limiting, or
T: growth in the presence of a antibiotic which can be sequestered by binding
T: harmlessly to some other protein). Gene duplication is by any measure an
T: increase of genetic material and it can be beneficial...
For examples along these lines, I'd recommend doing some MEDLINE searches
on the subject. For example, I browsed MEDLINE for 15 minutes on the web
at:
http://www.infotrieve.com/freemedline/
...and entered a search for "gene duplication" in the abstract and
"resistance" in the titles of papers. I chose to key on "resistance"
because I thought it would be more likely to pull out papers along
these lines. That's because understanding mechanisms of drug resistance
is of pressing importance in biomedical research -- meaning it interests
more investigators -- and because many of the mechanisms that lead to
resistance involve events that are frequently associated with gene
duplication. There are other areas and search topics that would
also pull out examples of "important" gene duplications but they are
more "spread-out".
Limiting the query from 1990 onward produced several interesting papers
which described how duplications produced and/or increased resistance
to various drugs and antibiotics. Sometimes these were duplications of
a few base pairs ("Tandem duplication in ermC translational attenuator
of the macrolide-lincosamide-streptogramin-B resistance plasmid pSES6
from Staphylococcus equorum." Lodder G; Schwarz S; Gregory P; Dyke K
(Antimicrob Agents Chemother, 40(1):215-7 1996 Jan)). Going back to
'90-'92, I found examples involving duplication of entire genes
("High-level resistance to ethidium bromide and antiseptics in
Staphylococcus aureus." Sasatsu M; Shibata Y; Noguchi N; Kono M, FEMS
Microbiol Lett, 72(2):109-13 1992 Jun 1). Other examples include even
larger duplications (partial chromosomes, extrachromosomal elements, etc).
Try other search combinations including "evolution", "expression", or
"mutation".
Interestingly, I found another article on an antarctic fish which
suggested it had seen expansion of a gene family (alpha-tubulins)
by duplication and divergence, which was possibly related to
cold adaptation.
If after this searching you truely cannot see any examples (including the
ones referenced above) of "positive mutations resulting from an increase
in genetic material", then perhaps we can pick a paper or two and go
over them.
Regards,
Tim Ikeda
tikeda@sprintmail.hormel.com (despam address before use)
PS - This topic has come up frequently here and elsewhere on the
net. I suppose it would be good to start collecting examples of
"beneficial gene duplications" for a talk.origins FAQ. If any other
biochemists out there have their "favorite" example, please feel free
to send me the journal, book or meeting reference.