Talk:Three-domain system

From Wikipedia, the free encyclopedia

	Biology Portal This article is within the scope of WikiProject Tree of Life, an attempt to better organise information in articles related to taxonomy and the phylogenetic tree of life. For more information, visit the project page.
Start	This article has been rated as start-class on the quality scale.
High	This article has been rated as high-importance on the importance scale.
Article Grading: The article has been rated for quality and/or importance but has no comments yet. If appropriate, please review the article and then leave comments here to identify the strengths and weaknesses of the article and what work it will need.

Contents 1 36s ribosomal unit 2 Typo? 3 Clean up terminology 4 Date Discrepancy 5 Viruses

[edit] 36s ribosomal unit

However, by comparing the 36S ribosomal subunit it is clear that Eukaryota are genetically closer to Archaea than Archaea are to Bacteria, suggesting an early evolutionary divergence between Archaea and Bacteria and a later branching of Eukaryota from Archaea. Chloroplasts and mitochondria which inhabit almost all eukaryota are known to have evolved from Bacteria.

This misses the entire point of the criticism. If Bacteria are paraphyletic to Archaea, and Archaea paraphyletic to Eukaryota, then it's only natural that archaeans should have closer sequences to eukaryotes than bacteria do. So it doesn't support the three-domain system over the alternative two-empire-one-paraphyletic system, as this suggests. The 36S ribosomal unit info could still be valuable, but I'm not sure how to work it in. Josh

[edit] Typo?

I'm no biologist, but shouldn't the word "eukaryotes" in the first line read "prokaryotes"? Rbraunwa 00:27, 21 July 2006 (UTC)

It should; fixed. Josh

[edit] Clean up terminology

I'd like to echo what this person says (below): please rewrite for the layman! Thanks!

I generally know about prokaryotes and eukaryotes, but I have no expertise in the field. I had to read the article several times to make sense of the terminology; it reads like one expert describing it to another, throwing around jargon loosely.

It would help to, 1) Clearly define the terms and their relationships to each other. Also putting all the terms in the graphic would help tremendously by providing a quick reference. 2) Simplify, simplify, simplify: Eliminate synonyms and re-use the same terms as much as possible. For example, just this phrase creates much confusion:

biologists like Mayr criticized him for over-emphasizing the uniqueness of the archaebacteria and ignoring strong genetic similarities between the groups

What are archaebacteria? Archaea? Bacteria? I looked at the graphic, but archaebacteria isn't there. I had to re-read the first paragraph (not a good sign) to find, ... originally called Eubacteria and Archaebacteria, which raised more questions: 1) They were originally called that: Are the terms obsolete? Why use them in the next paragraph? What are the proper terms? 2) Which term corresponds to what on the graph? Also, what exactly is a group? How does it relate to a domain?

I'm not asking for help -- I believe I figured it out. I'm asking that someone help the next non-expert reader. I would re-write it, but I'm not qualified.

Thanks, phrustrated in philly

[edit] Date Discrepancy

This article states that the Three Domain System was introduced in 1960. The article on Domains indicates 1990. Please correct the wrong one. Artworksmetal 18:51, 31 January 2007 (UTC)

For the record, that appeared to be vandalism and 1990 was correct. I fixed it before I saw this post. 66.92.53.49 22:12, 11 February 2007 (UTC)

[edit] Viruses

This is an interesting position. Viruses aren't considered a life-form therefore they do not belong to any of the three branches, but viruses themselves are defined as non-life because they depend on a pre-existing living organism to maintain themselves.... So viruses, deducing this logically, had to have evolved (come into being) after life-forms of some kind evolved; therefore viruses must have a starting point with one of the branches, they had to have been an offshoot of one of them and therefore a "branch off" of one of the branches. Can any one make an argument any other way? Nagelfar (talk) 03:05, 4 February 2008 (UTC)

There is a simple way to deal with this problem: the three-domain system applies to cellular life, and so viruses are excluded. There are some theories about DNA viruses playing an important role at the birth of the three domains (see Patrick Forterre, Proc Natl Acad Sci 103:3669-3674, 2006 doi:10.1073/pnas.0510333103), and are as ancient as the main cellular lineages, but I think that the question is outside the scope of this article (at least for its current size). Szentendrei (talk) 20:03, 5 February 2008 (UTC)

This point has been clarified more recently. Virus evolution - at least at the RNA/DNA sequence level has been too rapid for the standard evolutionary methods to resolve this problem completely. Having said that the current consensus is that viruses have co evolved with their hosts for most of their existence. Precisely when the viruses of these lines evolved seems unlikely to be answered in the near future. —Preceding unsigned comment added by 159.134.58.241 (talk) 15:54, 14 April 2008 (UTC)