Problems with Chromosomal Evolution - From Circular to Linear

I read your source and I think there are a few salient points to note.Firstly telomere resolvase' is, like 'telomerase' a descriptive title for whatever protein is actually performing the telomere resolution. Among the proteins they identify as capable of this is a topoisomerase, hadly an unknown. Similarly the specific E. coli phage TelN resolvase they identify is said to and has structural similarity to the integrase/ tyrosine recombinase proteins.Other proteins clearly exist which can resolve the cruciform Holliday junctions.The embo J. paper you go on to discuss may well be talking about a totally different 'telomere resolvase' it need not be the same as in the source paper, a similar possible confusion as to that between human and yeast telomerase.While the paper says that the resolvase is a site-specific recombinase rather than a general Holliday junction resolvase it is surely relevant to note that a general Holliday junction resolvase might well preform the samme basic function and be a very suitable substrate for a site specific enzyme to evolve from.TTFN,WK

This is obviously true for modern prokaryotes and eukaryotes but due to the differences mainly being due to structures the eukaryota are thought to have gained, most specifically the nucleus. Since the ancestor must either have had or not had a nucleus it must have been either pro- or eu- karyotic and the prokaryotic state is neccessarily the more primitive, although it is not neccessarily impossible that a prokaryotic bacteria could subsequently be derived from a eukaryotic ancestor.TTFN,WK

I don't see how that neccessarily follows. In that case you would have to be able to characterise your hypothetical common ancestor to show that it wasn't either pro- or eu- karyotic. And since being pro- or eu- karyotic basically depends on whether or not the cell has a nucleus, ther isn't much room for some in between sort of common ancestor.Why do you think your scenario is any less of a 'conundrum' than the eukaryotes being a divergent population from a prokaryotic base. A couple of answers to this, firstly because prokaryotes are the very first things in the fossil record. The first fossil evidence of life is of stromatolite cyanobacteria, the prokaryotes precede the eukaryotes by a couple of billion years. The second is the reason I previously mentioned, if the nucleus is the result of endosymbiosis then the original engulfing host cell must have lacked a nucleus and would therefore be prokaryotic by definition.TTFN,WK

Not just older. Also 'primitive' as opposed to 'derived', eukaryotes are a form of life derived from the prokaryotes. Primitve as in little evolved from or characteristic of an earlier ancestral type.My point has been that that ancestral type, the common ancestor of modern prokaryotes and eukaryotes, would have been a prokaryote.If you want to find the first common ancestor which wasn't a prokaryotic cell then you have to go to pre-cellular life.The first cell surely had to be a prokaryote (without a nucleus) but it didn't have to be a modern prokaryote.TTFN,WK