Giardia Bares All: Parasite genes reveal long sexual history

Science News Online ^ | Jan. 29, 2005 | Christen Brownlee

[js1138]

Giardia Bares All: Parasite genes reveal long sexual history

Christen Brownlee

While it hasn't yet been caught in the act, a single-celled parasite has been ready for sex for billions of years. A new research finding provides evidence that sexual reproduction started as soon as life forms that have nuclei and organelles within their cells branched off from their structurally simpler ancestors.

The parasite Giardia intestinalis is well known for causing a diarrheal disease that animals and people contract after drinking contaminated water. Many researchers consider this species to be one of the most ancient living members of the eukaryote, or true nucleus, lineage. However, unlike most eukaryotes, G. intestinalis and its relatives have been long considered to reproduce only asexually—by division into two identical cells.

To determine when reproduction via sperm and eggs originated, John Logsdon of the University of Iowa in Iowa City and his colleagues took a close look at G. intestinalis' mysterious reproductive life. They focused on the hallmark of sexual reproduction known as meiosis, the process that halves the number of an organism's chromosomes to make gametes such as sperm and eggs. Among available data on the G. intestinalis genome, the researchers searched for genes similar to those that control meiosis in other eukaryotes, including plants, animals, and fungi.

The researchers' analysis revealed that G. intestinalis possesses genes similar to those used for meiosis by other eukaryotes. At least 5 of those genes function only in meiosis, and 10 others have roles both in meiosis and other functions, Logsdon's team noted in the Jan. 26 Current Biology.

Although the researchers didn't establish that G. intestinalis reproduces sexually, Logsdon notes that a discreet sex life might turn up after further study. "Lack of evidence is not evidence of lack," he says.

On the other hand, the findings suggest that meiosis was established early in eukaryotic evolution, making sexual reproduction "a very central feature of being a eukaryote," says Logsdon. Bacteria and other simple-celled life forms, or prokaryotes, don't make eggs and sperm.

All living eukaryotes, including G. intestinalis, share numerous cellular features and processes that aren't seen in prokaryotes. According to Andrew Roger of Dalhousie University in Halifax, Nova Scotia, establishing that all eukaryotes are capable of meiosis could "make the evolutionary transition from prokaryote to eukaryote even more difficult to sort out.

"A lot had to happen when eukaryotes evolved. Why aren't there any intermediate stages of this process alive today? Did all the intermediate forms go extinct, and why?" Roger asks.

Logsdon says that he and his team plan to continue their research by looking for meiosis genes in other eukaryotes thought to be asexual.

References:

Ramesh, M.A., S.-B. Malik, and J.M. Logsdon Jr. 2005. A phylogenomic inventory of meiotic genes: Evidence for sex in Giardia and an early eukaryotic origin of meiosis. Current Biology 15(Jan. 26):185-191. Abstract available at

http://dx.doi.org/10.1016/j.cub.2005.01.003.

Sources:

John M. Logsdon Jr. University of Iowa Department of Biological Sciences 310 Biology Building Iowa City, IA 52242-1324

Andrew Roger Department of Biochemistry and Molecular Biology Dalhousie University Halifax, NS B3H 1X5 Canada

http://www.sciencenews.org/articles/20050129/fob1.asp

From Science News, Vol. 167, No. 5, Jan. 29, 2005, p. 67.

[js1138]

Oh please. Such "evidence" would be widely disputed by today's Darwinists, lets not go there.

Instead, lets go for evidence that *won't* be disputed: code skipping.

Pick 3 species. Find genetic code that exists in what Evolutionary Theory would say have been in both an earlier and a modern species, but that skips entirely a species that Darwinists claim came in between the two.

Interesting. Where has this happened? Examples?

[furball4paws]

Explain to me what a "favorable mutation" is.

Here's a couple more facts.

1. The average bacterium has, say 3000 genes. If you have 1,000,000 mutants in your flask, most of those genes were hit more than once. There are some parts of the genome where mutations occur at very high frequencies, and some other areas where the frequencies are considerably lower.

2. A mutation is a change in the DNA sequence. Most mutations have no visible effect on the bacterium. A few mutations will be lethal, but you won't see those under normal circumstances, the bug just dies. The rest are "neutral" or "beneficial" or "not beneficial", but not lethal, etc.. See why I need to know what you mean by "favorable"?

[Paulus Invictus]

We were told by Park Rangers that giardia now lives happily in most US water sources. It has been spread by cattle and sheep who deposit the parasites everywhere, including around water sources. People drinking out of high mountain springs in the Sierras are sure to get the disease and it's no fun. Drink Coke and you'll be OK (except for a high caffeine and sugar load).

[js1138]

A few drops of Clorox will help. There are tablets for hikers and campers.

[furball4paws]

"a) what the hell do those PCB-eating bugs excrete?
b) I imagine metabolizing conjugated systems leads to
all kinds of free radical production; how do they
deal with it?
and a third:
c) Has anyone thought of getting "two for the price of
one" for the PCB-eating bugs and engineering further
enzymes so they excrete industrially useful
feedstock or intermediates? "

a. The ultimate end product of these bugs is mineralization of the PCB, so you would get water, carbon dioxide, and in the case of PCB's, chloride ion + bug bodies. Anything less than mineralization runs the risk of the bugs "excreting" something worse than the starting compound.

b. bugs have many ways of protecting themselves from free radicals, but if my memory serves me, free radicals are only a small part of degrading these chemicals. BTW the bugs are often "consortia" not individual species.

c. Looking for something for nothing? While I'm not going to say a definitive "No", I am still going to say "No". There's no free ride, even in the bug world. Besides PCB's, as you know, are not one Chemical but a mixture and they are very water insoluble. It would be very difficult to get a pure product from such a mixed feedstock.

[Southack]

Evolutionary Theory completely and totally breaks down in the face of genetic code skipping. DNA that skips an entire intermediate species falsifies Evolution...and it can't be argued otherwise by even the most rogue-ish and obstinate of Darwinists. - Southack

"Interesting. Please elaborate. I remember reading something about this a year or so ago, but I've looked and there's not much information available. Thanks, MM"

Mapping genomes is just now giving us the raw data required for this proof/disproof.

Pick 3 sequentially "evolved" species with the same alleged common ancestor. The oldest species A has "gene 451." Species A supposedly branches into Species B, which has no trace of gene 451. Species B then purportedly branches into Species C, which *has* gene 451.

That would be code skipping, something beyond the ability of Common Descent to explain; it would falsify, conclusively, Evolutionary Theory (though no doubt the last holdouts of Darwinism will retreat to a viral defense to attempt to explain such code skipping)...

...On the other hand, we see code skipping in intelligently designed software all of the time. Re-using old code, even years later, is common, though numerous software programs written in between such re-uses of particular code won't always have such programming routines.

Code skipping is therefor common under ID, but ridiculous under ET. Genes that have disappeared in one species do not suddenly re-evolve back into a new child species.

[Southack]

Pick 3 species. Find genetic code that exists in what Evolutionary Theory would say have been in both an earlier and a modern species, but that skips entirely a species that Darwinists claim came in between the two. - Southack

"Interesting. Where has this happened? Examples?" - JS1138

I'll take up that burden if you'll first be willing to post, in black and white, that you agree with the stated concept. Specifically, that genetic code skipping conclusively and irrefutably disproves Evolutionary Theory.

[js1138]

I am not a biologist and do not know all the technicalities, but I agree in principle that DNA evidence could disprove common descent. This principle has been stated numerous time on these threads, always by evolutionists.

But there's a problem with the specific way you've stated your case. Darwin published 145 years ago, knew absolutely nothing about genetics -- a concept not yet invented, and classified descent by morphology. So the answer to your your question, in the exact words you have used, is no.

[Southack]

"Darwin published 145 years ago, knew absolutely nothing about genetics -- a concept not yet invented, and classified descent by morphology. So the answer to your your question, in the exact words you have used, is no."

How does morphology explain fully functional genetic code skipping?

[houeto]

"A lot had to happen when eukaryotes evolved. Why aren't there any intermediate stages of this process alive today? Did all the intermediate forms go extinct, and why?" Roger asks.

Is there a missing plantanimal here?

[js1138]

How does morphology explain fully functional genetic code skipping?

Errors in 145 year old classification? Other than that I give up. Show me the examples.

[Southack]

Examples mean nothing when we disagree over their significance.

If you can't agree that code skipping disproves Evolutionary Theory, then there's no reason for me to bother throwing out examples of code skipping (that would simply open me up to further attacks while offering no chance of eventual agreement).

[js1138]

I have agreed in principle that code skipping would be troublesome. I am not a biologist, so I can't evaluate how troublesome a particular instance would be. I might say that if you are a sincere Christian, you would not consider a bit of bother excessive if it would save someone. That would be incredibly vain.

What you need to agree to is that you will not attempt to apply this principle to things that have historically been misclassified.

[Southack]

"I might say that if you are a sincere Christian, you would not consider a bit of bother excessive if it would save someone. That would be incredibly vain."

Lets stay focused on science, please.

[js1138]

Fine, then don't inject your personal problems into the discussion. If there are examples of skipped code, show them. No one is getting paid for this.

[jwalsh07]

I've been able to deduce that Spetners calculations were sent in a letter to Dr. James Crowe, University of Wisconsin. His email address is here.

Good luck.

[jwalsh07]

I know there is a mechanism called "back mutations" which can restore lost information such as your hypothetical gene 451. What I don't know is the rate at which such mutations occur. Any idea?

[jwalsh07]

Explain to me what a "favorable mutation" is.

As a layman, I'd say one that adds information to the genome but like I said, I'm a layman. :-}

[Southack]

"I know there is a mechanism called "back mutations" which can restore lost information such as your hypothetical gene 451. What I don't know is the rate at which such mutations occur. Any idea?"

Back mutations can't restore a gene that is completely missing in a species.

[jwalsh07]

OK, gotcha, the entire gene is missing, not that the gene is missing information.