How Sex May Have Started it All
Birds do it, bees do it, even strands of As, Us, Cs, and Gs do it
By Jack Lucentini

ROILING IN RECOMBINATION Supporters stand by their findings. Recombination
"may have played a role in the origins of life," says Niles Lehman,
associate professor of chemistry at Portland State University in Oregon. He
cites as evidence a finding from his laboratory that RNA molecules, possibly
similar to precursors of modern genes, can catalyze recombination.1 He also
points out new research that suggests bacteria can fully merge their genomes
in a process that has striking similarities to some aspects of sexual
reproduction.2

Some researchers doubt, however, that these findings are significant for
explaining how sex evolved or contributed to life's origins. Lehman's
arguments "are based on poorly defined, poorly distinguished processes,"
says Rosemary J. Redfield, associate professor of zoology at the University
of British Columbia, Vancouver. True sex, which has been defined as syngamy
(gamete fusion), nuclear fusion, and meiosis,3 is commonly regarded as
unique to eukaryotes. Simpler organisms, mainly bacteria, conduct
"parasexual" or sex-like activities involving limited exchange or uptake of
genes, but these processes are largely distinct from reproduction.
Nevertheless, they do include many of the same mechanisms of recombination,
or DNA exchange, found in sex.

SEX IN VITRO The standard view took on a new dimension in 1998 when Carl
Woese at the University of Illinois, Urbana-Champaign, concluded that gene
exchange among the earliest cells was so rampant that the concept of a
single first organism is meaningless. "The universal ancestor is not a
discrete entity. It is, rather, a diverse community of cells," he wrote.4

Lehman says this concept should be taken further, to not only the first
cells but also to their forebears, such as the naked, self-replicating RNA
molecules that some researchers believe preceded them. These molecules had
to be complex enough to catalyze their own replication, but they couldn't
become complex without first undergoing repeated cycles of replication and
selection, a chicken-and-egg conundrum that remains an outstanding
biological riddle.

Recombination could help solve it, Lehman argues.5 Depending on the position
of recombination points, sequence swapping can lengthen one molecule and
shorten another. Lehman says repeated cycles of this process could build
complex molecules far more quickly and efficiently than polymerization, the
process usually presumed to have created them. Polymerization would involve
adding nucleotides to the molecules one by one. For struggling
proto-organisms, this might be like trying to create a coherent novel by
adding one random letter at a time.

Read the rest at The Scientist.com
http://www.the-scientist.com/yr2004/mar/research4_040329.html

Comment:
The function of sex includes gene shuffling from two sources.  But genes are
shuffled even by clonal species.  Sex raises the recombination of genetic
material to another level, that's all.

Posted by
Robert Karl Stonjek.
---
þ RIMEGate(tm)/RGXPost V1.14 at BBSWORLD * Info{at}bbsworld.com

---
 * RIMEGate(tm)V10.2áÿ* RelayNet(tm) NNTP Gateway * MoonDog BBS
 * RgateImp.MoonDog.BBS at 3/27/04 7:45:26 PM