On 1/12/2011 2:40 AM, Invisible wrote:
>> This in fact happens. We can even, in many cases, parse out what those
>> *where*, sometimes by finding those extra structures still intact in
>> other species.
>
> More to the point, biological structures can *change purpose* too.
>
>> And you are dead wrong on the later, evolution **keeps**
>> masses of junk, whether it produces a benefit or not.
>
> That too. The human genome has half a dozen broken copies of the globin
> gene, for example. (Plus 4 (?) similar but not identical copies that
> actually work.)
>
>> The single cell do not, in general, contain mitochondria.
>
> False.
>
> Note carefully that "single-celled organisms" covers a vast variety of
> life forms, only some of which are closely related. Many of these
> contain mitochondria, and many do not. The fact that they are
> unicellular does not correlate particularly well with the presence of
> absence of mitochondria.
>
> The distinction you're looking for is between eukaryotes and
> non-eukaryotes.
>
Uh, yeah. Couldn't think of the proper term though. But, the rest is 
correct. If you don't have excess resources to waste on messing with 
extra baggage, you don't live long if you have it. If you do have the 
"power plants", you can afford to waste more space in the genome on 
things that don't work, duplicate results, etc.

>> Their genetics are often **far** more streamlined, because
>> they can't afford to carry junk around, which doesn't do anything, for
>> the reason you describe. It costs resources. Having a sort of "power
>> plant" in the cell, whose genetics are 100% geared at producing excess
>> amounts of energy, over what is absolutely needed by themselves, allows
>> the rest of the genome, in the main cell, to be very sloppy in its
>> operations, copying, cleanup, etc. Anything with such an internal power
>> plant can afford to keep lots of stuff that does nothing at all, and
>> only gets rid of things that are actively defective, usually not by
>> deletion, but just by shutting them off, so they do nothing. This allows
>> for what, in a single cell, would be egregious errors, such as making an
>> exact copy of a sequence, then later having that sequence get mangled
>> into a unique function. Its way harder to manage that if you can't
>> afford extra copies lying around, where your energy input is drastically
>> damaged, if you allow such a copy to happen.
>
> I'm not sure I actually agree with this assessment.
>
http://scienceblogs.com/pharyngula/2010/12/how_to_afford_a_big_sloppy_gen.php

As to the cite for prokaryotes not having as many copy errors, I think 
it would be more accurate to say, "They don't *preserve* as many." If 
they did, they would have way more junk DNA, which is precisely what 
they can't afford to have laying around in the first place. The actual 
number of such errors that happen is likely the same, but, when it comes 
to costs, if you can't afford them, you don't see those copied chunks 
sticking around long.

-- 
void main () {

     if version = "Vista" {
       call slow_by_half();
       call DRM_everything();
     }
     call functional_code();
   }
   else
     call crash_windows();
}

<A HREF='http://www.daz3d.com/index.php?refid=16130551'>Get 3D Models, 
3D Content, and 3D Software at DAZ3D!</A>

Post a reply to this message