While I am quite backlogged on several threads I did come by something in
some further research of parasitic plants and "vestigial" genomes.
Plasmodium falciparum (the human malaria parasite) is a parasitic protist
from the "hodge-podge" Phylum Apicomplexa which contains numerous other
digenetic parasites (two host parasites, eg. human, mosquito; tick, cattle
etc..). Plasmodium as well as numerous other genera contain two organellar
DNA, one is mitochondrial and the other a small circular molecule (35kb in
Plasmodium). The 35kb molecule has been sequenced and the genes
characterized the genome is very plastid-like (in sequence and gene
content). The genes found are nearly all those found in a photosynthetic
plant chloroplast DNA except the lack of any photosythetic genes. The
highly conserved 16S and 23S ribosomal DNAs are are clearly of "plastid
origin" as green algal and plant ribosomal genes have clearly distinguished
conserved nucleotide sequences and unique secondary structural features.
This data fits the hypothesis held for such things as parasitic plants in
that when the ability to do photosynthesis is lost the photosynthetic genes
are randomly lost over time resulting in a reduction of the size of the
cpDNA genome. In addition the nucleotide sequence itself becomes highly
mutated (presumably due to loss of selectional pressure from loss of
function). Parasitic plant with very close "green" relatives show
relatively uneffected genomes (ie. few genes lost or maybe only a few
mutations resulting in loss of photosynthetic ability) but parasitic plants
(such as Raflessia) that have no known relations with any other extant
plants exhibit wildly reduced cpDNA genomes and highly divergent sequences.
Astasia (thought to be a sister genus to Euglena, a very unique
protist with many "animal like" feature but having a chloroplast) is
nonphotosythetic but also has a cpDNA genome that is very similar to Euglena.
Plasmodium, seems to represent the ultimate in genome reduction.
All photosynthetic genes are lost. Obviously alternative hypotheses are
possible: they may have never had the photosynthetic genes, plants gained
the photosynthetic genes. The interesting thing here is the striking
similarity of this DNA in a non-photosynthetic parasitic protist that is
carrying around a plastid-like genome. There is strong evidence that the
genes that remain are functional (transcription of these genes occurs) thus
the remains of this plastid-like genome likely retains a function.
This by itself may not seem too crazy but the fascinating part is
that several years ago sequence comparisons of the nuclear ribosomal DNA's
found a very high similarity between the DNAs of apicomplexins with several
photosynthetic protists including the red algae. One gene and another open
reading frame (ORF) in this plastd-like genome were very similar to genes
found in red algal plastids. I would venture to say here that the
unexpected observation that nuclear sequences were similar to sequences of
photosynthetic plants (despite tremendous numbers of existing
non-photosynthetic protists groups) and then the discovery of "remnant
plastid-like" genomes in these same organisms are independent confirmations
of a hypothesis that Plasmodium and many other Apicomplexins had algal
ancestors: effectively malaria is an animal that formerly was a plant (both
in the broadest of descriptions).
As a tangent, these parasitic protists got me thinking about the
origins of parasites and preservation of them. Issues abound (and I'm sure
many more that I haven't thought of) and here are just a few that come up in
my mind:
1: Concerning YEC's: At what point did the relationships of these
parasites with their hosts arise (this could even be expanded to viruses
etc.). Lots of origins questions here!!! I was amazed to find out how many
different digenetic parasites (a very peculiar life-cycle to say the least)
there are and I wondered how were these preserved on the ark. If they
simply were carried though in one of the hosts the number of parasites that
would have had to been carried by two dogs/cows/etc.. would have had to been
tremendous - they would have been a bunch of really sick puppies (no pun
intended). Possibly it could be argued that there was a large population of
ticks and mosquitoes on the boat which wouldn't be unreasonable.
2: Problematic to me is the specificity that many of these parasites have
for a human host to complete the cycle. What does this say about the age of
man. Again, did Noah and his family carry a multitude of diseases with them
or did they originate after the flood (this would seem problematic in a
4000year old earth. I wonder if anyone knows anything something of the
history of malaria?
It would seem to me that a long time would be required for organisms to
adapt themselves to the human host. The other alternative I think is that
disease is a special agent of God "created" for a special purpose. I don't
know, maybe there is some juicy stuff here for those tired of talking
Neanderthals.
Joel
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