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Re: Welcome to a 'Fragile X ' Universe *LINK*

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The Regressive Hypothesis

In contrast to the progressive process just described, viruses may have originated via a regressive, or reductive, process. Microbiologists generally agree that certain bacteria that are obligate intracellular parasites, like Chlamydia and Rickettsia species, evolved from free-living ancestors. Indeed, genomic studies indicate that the mitochondria of eukaryotic cells and Rickettsia prowazekii may share a common, free-living ancestor (Andersson et al. 1998). It follows, then, that existing viruses may have evolved from more complex, possibly free-living organisms that lost genetic information over time, as they adopted a parasitic approach to replication.

Viruses of one particular group, the nucleocytoplasmic large DNA viruses (NCLDVs), best illustrate this hypothesis. These viruses, which include smallpox virus and the recently discovered giant of all viruses, Mimivirus, are much bigger than most viruses (La Scola et al. 2003). A typical brick-shaped poxvirus, for instance, may be 200 nm wide and 300 nm long. About twice that size, Mimivirus exhibits a total diameter of roughly 750 nm (Xiao et al. 2005). Conversely, spherically shaped influenza virus particles may be only 80 nm in diameter, and poliovirus particles have a diameter of only 30 nm, roughly 10,000 times smaller than a grain of salt. The NCLDVs also possess large genomes. Again, poxvirus genomes often approach 200,000 base pairs, and Mimivirus has a genome of 1.2 million base pairs; while poliovirus has a genome of only 7,500 nucleotides total. In addition to their large size, the NCLDVs exhibit greater complexity than other viruses have and depend less on their host for replication than do other viruses. Poxvirus particles, for instance, include a large number of viral enzymes and related factors that allow the virus to produce functional messenger RNA within the host cell cytoplasm.

Because of the size and complexity of NCLDVs, some virologists have hypothesized that these viruses may be descendants of more complex ancestors. According to proponents of this hypothesis, autonomous organisms initially developed a symbiotic relationship. Over time, the relationship turned parasitic, as one organism became more and more dependent on the other. As the once free-living parasite became more dependent on the host, it lost previously essential genes. Eventually it was unable to replicate independently, becoming an obligate intracellular parasite, a virus. Analysis of the giant Mimivirus may support this hypothesis. This virus contains a relatively large repertoire of putative genes associated with translation genes that may be remnants of a previously complete translation system. Interestingly, Mimivirus does not differ appreciably from parasitic bacteria, such as Rickettsia prowazekii (Raoult et al. 2004).

Messages In This Thread

White Female Supremacy? *LINK*
Welcome to a 'Fragile X ' Universe
Re: Welcome to a 'Fragile X ' Universe *NM* *LINK*
Re: Welcome to a 'Fragile X ' Universe *LINK*
Re: Welcome to a 'Fragile X ' Universe *LINK*
Re: Welcome to a 'Fragile X ' Universe *LINK*
Re: Welcome to a 'Fragile X ' Universe
Re: Welcome to a 'Fragile X ' Universe
Re: Welcome to a 'Fragile X ' Universe
Feed them Truth; they'll liberate themselves
Re: Welcome to a 'Fragile X ' Universe *LINK*
Re: Welcome to a 'Fragile X ' Universe *LINK*
Re: Welcome to a 'Fragile X ' Universe *LINK*
Re: Welcome to a 'Fragile X ' Universe *LINK*
Re: Welcome to a 'Fragile X ' Universe *LINK*
Re: Welcome to a 'Fragile X ' Universe *LINK*
Re: Welcome to a 'Fragile X ' Universe
Natural Selection vs Human Choice
The sins of the father *LINK*
Re: The sins of the father *LINK*
Re: The sins of the father *LINK*
Re: The sins of the father
Neanderthal DNA lives on ... in some of us *LINK*
Re: Neanderthal DNA lives on ... in some of us *LINK*
Re: Neanderthal DNA lives on ... in some of us
More autistic expressions... *LINK*
'Give a monkey a brain...
Derek Fisher's baby girl *NM* *LINK*
Re: The sins of the father *LINK*
Re: The sins of the father *LINK*
More Euro-Science *LINK*
More Autism Diagnoses in High-Tech Areas... *LINK*
fascinating.
Re: fascinating. *LINK*
Re: fascinating.
Super-social gene may hold clues to autism, other *NM* *LINK*
Supremely Social *LINK*
Re: The sins of the father *LINK*
Re: Welcome to a 'Fragile X ' Universe *LINK*
Re: Welcome to a 'Fragile X ' Universe
Re: Welcome to a 'Fragile X ' Universe *LINK*
Tell us how you really feel... *LINK*
Re: Welcome to a 'Fragile X ' Universe *LINK*
Re: Welcome to a 'Fragile X ' Universe *LINK*
Re: Welcome to a 'Fragile X ' Universe
Re: Welcome to a 'Fragile X ' Universe *LINK*
Re: Welcome to a 'Fragile X ' Universe
Re: Welcome to a 'Fragile X ' Universe
Re: Welcome to a 'Fragile X ' Universe *LINK*
Re: Welcome to a 'Fragile X ' Universe
The Scion vs the Seed
Re: The Scion vs the Seed *LINK*
Re: The Scion vs the Seed
Re: The Scion vs the Seed *LINK*
Re: The Scion vs the Seed *LINK*
Re: The Scion vs the Seed *LINK*
Re: The Scion vs the Seed *LINK*
Re: Welcome to a 'Fragile X ' Universe
Re: White Female Supremacy?
Re: White Female Supremacy?
Re: White Female Supremacy?
Re: White Female Supremacy?


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