chop chop chop chop chop chop (that's me chopping)
>Actually, the thing I found so surprising about that tape and Dawkin's
>supposed reply, there is a phenomenon called polyploidy which does increase
>the information content of the daughter plant. It was this phenomenon,
>which is known by any biologist, that first made me suspicious of the tape.
>Dawkin's should have been able to mention it directly. The fact that I, a
>geophysicist, could think of it made me wonder why Dawkins, a biologist
>didn't. Here is what happens. Two species with different chromosome
>numbers can cross producing a gamete which usually dies. but once in a
>while the crossed plant doubles the number of chromosomes and produces a
>fertile species with the entire genetic material from both parent species.
>This daughter species is unable breed with the parent species. The daughter
>species represents a species with more genetic information than either of
>the parents! So, the tape is wrong in its claim that no case exists. I
>quote from Boxhorn's Speciation FAQ on Talk Origins
Following up on what I previously posted regarding increases in information
in the DNA. Though I am unsure what is being implied by this I would just
offer another example of increased complexity that I don't think I have seen
posted on this group before. Typically polyploids are given as a textbook
case of increased information content and while I think that is perfectly
legitimate I think there are more pertinent examples to be found.
I could name several similar examples but will stick to one for the present:
Chlorarachniophytes are marine protists that have an interesting organellar
morphology. Essentially Chlorarachniophytes contain organelle that has FOUR
MEMBRANE walls.
A cross section through a Chlorarachniophyte would look something like:
__________________ Outer membrane
-------
| | Nucleus of the Chlorarachniophyte
-------
------------ membrane
------------ second membrane
-------
| | highly reduces eukaryotic nucleomorph (380 kb)
-------
------------ third membrane
------------ fourth membrane
Chloroplast (third and fourth membrane surround the chloroplast)
------------ first
----------- second
----------- third
----------- fourth
cytoplasm of chlorarachniophytes
___________ outer membrane
So these organisms essentially have TWO eurkaryotic nuclei and a four
membrane bound chloroplast. How did this arrangement come about. It seems
quite apparent that this heterotrophic organism engulfed a green algae. The
first two membranes then would be the outer membrane and the outer membrane
of the green alga. Inside the second membrane then is the original nucleus
of the green algae and then the third and fourth membranes represent the
double membrane of the chloroplast of the alga.
This is not just an endosymbiosis anymore because these organisms cannot be
separated from one another. The nucleus of the alga has been drastically
reduced having though it retains its own ribosomal DNA genes which CLEARLY
identify the inner nucleus as that of a green alga (also the nuclear
ribosomal genes of the amoeboflagellate host cell are clearly not related to
green algae).
So this is an example of REDUCTION of genome information but an even more
important example of and INCREASE in information content. Now, rather than
being heterotrophic this organism has ACQUIRED photosynthesis. Genes from
the chloroplast and likely the nucleus has been transferred to the host
nucleus. The chloroplast of the Eukaryotic endosymbiont of this eukaryotic
cell is a completely integrated part of the host as much as a mitochondria
is part of all of our cells. This is quite a jump in complexity and
information and there are many many other examples that include triple
membraned organelles, bi-nucleated cells, etc.. all of which are in the
process of both reduction of some contents while resulting in an overall
increase in complexity.
One other example that is might interest some are the bacterial
endosymbionts of aphids. Here is a case that is virtually a snapshot of the
evolution of mitochondria caught in an intermediate step of evolution. See
reference for more info.
I'll provide more refs later when I get a chance to go through my files.
Joel Duff
The most accessible and readable refs are:
Baumann, P., N. A. Moran, and L. Baumann. 1997. The evolution and genetics
of aphid endosymbionts. BioScience 47(1): 20
Gilson, P. and G. I. McFadden. 1997. Good things in small packages: the
tiny genomes of chlorarachniophyte endosymbionts. BioEssays 19(2): 167-173.
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