Re: Article] Complex genomes evolved by chance

in article [EMAIL PROTECTED], Robert Karl Stonjek at
[EMAIL PROTECTED] wrote on 25/11/03 12:30 PM:

> Genome complexity
> Complex genomes evolved by chance
> By Cathy Holding
> 
> The question of whether the evolution of large and complex genomes in
> complex multicellular organisms is due to natural selection or simply a
> function of chance has been the subject of considerable debate. In November
> 21 Science, Michael Lynch and John Conery at Indiana University argue that
> the inclusion of intragenic spacers-introns-and transposons, coupled with
> the increase in gene number associated with genomes of multicellular animals
> and plants, were not essential for adaptive phenotypic diversification
> during eukaryotic evolution, but are the result of orders-of-magnitude
> reductions in population size. This process magnified random genetic drift
> and prevented "purifying" natural selection from removing them (Science,
> 302:1401-1404, November 21, 2003).
> 
> "Drawing from the now enormous databases provided by full-genome sequences,
> we have attempted to develop (and test) a general theoretical framework for
> explaining the expansion in genomic complexity (including numbers of genes,
> numbers and sizes of introns, and numbers of mobile elements) in the
> transitions from prokaryotes to unicellular eukaryotes to multicellular
> eukaryotes," Lynch told The Scientist in an E-mail.
> 
> "We argue that much of the 'syndrome' of genomic complexity arose not
> because of direct selection for such change but because a reduction in
> population size diminishes the efficiency of natural selection against
> various types of genomic insertions," he said.
> 
> Laurence Hurst, professor of evolutionary genetics at the University of Bath
> explained, "If we ask the question why might a new mutation (a point
> mutation, an insertion, deletion, duplication, whatever) go from rare (which
> at first it must be) to common (aka, fixation), then, in principle, there
> are two answers: either selection favored it or it got there by chance
> (drift)," he told The Scientist by E-mail. "If a population is huge, it will
> take ages and many chance steps for a given new weakly deleterious mutation
> to get to fixation. In a small population, it takes just a few lucky steps."
> 
> The mathematics in the paper are based on the effective population size, Ne.
> "Generally, if the mutation reduces fitness by a small amount(s), then it
> will be eliminated if s>>1/ Ne. If s is about 1/ Ne, it stands a pretty good
> chance of getting to fixation. So as Ne goes up, an ever smaller number of
> slightly deleterious mutations can get to fixation by chance," Hurst wrote.
> "The authors say that as organisms get big, they also have low Ne. We have
> introns, but small eukaryotes do not, not because they are good for us but
> because our population size is too small for us to stop them accumulating."
> 
> Read the rest at The Scientist.com:
> http://www.biomedcentral.com/news/20031124/03
> 
> Kind Regards,
> Robert Karl Stonjek.
> 
>

 I think the origins of genomic complexity are better described in this
http://www.applied-evolution.co.nz/selfishH/selfish_helper.ssi

But hen I would say that.

-- 

Phillip Smith
phills@(buggger).co.nz replace bugger with ihug
http://www.applied-evolution.co.nz


"he who is smeared with blubber has the kindest heart" -- a Greenland Eskimo
adage