Correction - Re: Increasing information?

Sun, 7 Jun 1998 06:32:39 -0500

Earlier I wrote:
>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 an 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

This obviously should be reversed in sequence!!

>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.
>Joel and Dawn Duff ,-~~-.___.
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