Re: Article] Complex genomes evolved by chance

Robert Karl Stonjek <[EMAIL PROTECTED]> quoted:

[ Re: http://www.biomedcentral.com/news/20031124/03 ]

> 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. [...]

> 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."

If we ask the question why might a new mutation go from rare to common
then, in principle, there are at least three answers:

1. selection favored it;
2. it got there by chance;
3. It was in linkage disequilibrium with something selection *did* favour.

This isn't just a minor nitpick - the effect of the third point can be
a large one.

Consider the fact that much constructive evolution takes place by
duplication and then variation of one of the copies.  If a variation
in one of the copies proves beneficial, then the rest of the duplicated
section can be dragged along for the ride - through virtue of being
linked to it.

Linkage is at its strongest when we are talking about whole chromosomes -
where there is no easy way for unlinking to happen - but can be a
substantial factor elsewhere.
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