(X) Something else to point out: much of the genetic research in
fishes has been driven by the hope that fisheries managers can find some
useful tool for discriminating among fish stocks. Ideally, these
markers would be neutral with respect to natural selection, so that
their presence or absence would be due solely to the relatedness of
individuals, rather than some environmental variable. So far, each of
the genetic tools (chromosomal structure, allozymes, mitochondrial DNA,
and microsatellite sequences) that have been discovered and applied have
been found to not be neutral, i.e. have some selective importance.
Actually, microsatellites may be all right, but there's evidence from
some human diseases that they may not be neutral either. The point is,
when we can observe variation being lost with the genetic tools
available, we're seeing it being lost for sequences / proteins / traits
that probably ARE important for how the organism relates to its
environment! This is VERY different from "random noise" mutations.
I apologize for such a long-winded sermon - the problems surrounding
loss of genetic diversity are actually a LOT more complex than this,
but the misconception that lost diversity will take care of itself is
fairly common, and extremely dangerous. Although new species MAY form
eventually, the present ones are certainly disappearing at a faster rate
than they can be replaced. The same problem of decreasing genetic
diversity in those species that are declining or endangered makes the
odds for their survival a lot poorer.
I hope that this helps.
Regards,
Chris Wilson.
_______________________________________________________________
>This is a comment on an ACN-L discussion from several weeks ago, which
>I am only just now reading:
>
>At 06:08 PM 4/1/96 -0700, peter.unmack at ASU.Edu wrote:
>>My understanding of genetic theory indicates that once a species loses
>>genetic diversity it isn't re-created.
>
>I have heard this, but I have also heard the opposite: that genetic
>diversity is almost always re-created. That argument went like this:
>Genetic mutations are not random: certain mutations happen over and
>over again, because that particular DNA change is easier to trigger.
>Coversely, other DNA changes are much harder to trigger. Therefore,
>if a mutation (say: A -> A') has happened once, it will likely happen
>again. So even if all the A' fish die, more will mutate. (Obviously,
>we're talking about whole populations of fish, over a period of years
>or
>longer.)
>
>I do not have the biology background to argue this point, but perhaps
>someone
>else does? This point is relatively important for captive breeding
>programs.
>If it were true, then the discussions about maintaining genetic
>diversity
>would be moot. If the fish survived, the genetic diversity could be
>largely
>regenerated.
>
>Joshua Levy <joshua at intrinsa.com>
>
>