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progenitor gene

Andrew J. Roger roger at evol5.mbl.edu
Fri Jun 20 06:42:16 EST 1997

Susan Hogarth wrote:
> higginss at VAX.CS.HSCSYR.EDU wrote:
> >
> >... Also, what extant
> > organism is considered the most ancient.
> Could you explain what this means? On the surface, the question seems to
> be "What is the oldest thing still living?", but I suspect you mean
> something different...

I suppose it could mean: what living organism displays the most
retained ancestral features of the latest common ancestor of
all life?  I think this could be a reasonable question.  My
bet is that eubacteria, in general, probably are most similar
to the latest common ancestor of life in their overall cellular
architecture-- they prokaryotic cells with ester-linked fatty-acyl
lipids, with a circular chromosome and genes organised into 
operons. It seems that the cenancestor (most recent common
ancestor) probably had all of these features if one accepts
the following tree:
								Ester/Fatty-acyl  Circ chromo   Operons
     _____ Eubacteria				YES				YES			YES
---/   ___ Archaebacteria			NO				YES			YES
   \  /
      \___ Eukaryotes				YES				NO			NO

Of course the overall similarity of an organism to an ancestor will
depend on what characters you choose to evaluate AND how you weight
the various characters.

Andrew J. Roger

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