One origin? (viral evolution)
jcclark at CSUPOMONA.EDU
Fri Jul 20 09:54:13 CDT 2001
At 07:43 AM 7/20/01, Thomas Lammers wrote:
>At 08:11 AM 7/20/01 -0600, you wrote:
>>No, prokaryote and eukaryote refer to the nucleus. Karyo means "nut", and
>>that's what Hook and others thought it looked like. "Eu" means "true", so
>>the eukyaryotes have a "true nut" or true nucleus.
>Well, of course the term refers to the nucleus, but the point is whether a
>*cell* has a nucleus or not! Who cares if non-cellular things have a
>nucleus? If we consider viruses to be prokaryotic, then so is a quartz
>crystal or a diamond. Not having a nucleus is really a moot point when you
>don't have a cell membrane, cytoplasm, ribosomes, or metabolism!
And now, for a flaming cladist viewpoint!
Snakes are tetrapods, even though they have no legs, because they are
members of the tetrapod clade, descended from the first tetrapods.
Likewise, eukaryotes are a clade, and eubacteria may be a clade (although I
know that Ken disagrees), but "prokaryotes" are a grade.
If a mammalian virus is a piece of mammalian DNA gone astray, it is a
eukaryote, and in fact it is a mammal. Viruses being what they are, they
have little trace of their ancestry, but I would venture that the
differences in gene regulation and genome structure between eubacteria and
eukaryotes might be reflected in viral genomes, and that we could thus
understand their relationships.
"Defining" prokaryotes and eukaryotes by their nuclei is essentialist.
Let's instead ask what we can infer about lineage groups.
Curtis Clark http://www.csupomona.edu/~jcclark/
Biological Sciences Department Voice: (909) 869-4062
California State Polytechnic University FAX: (909) 869-4078
Pomona CA 91768-4032 USA jcclark at csupomona.edu
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