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Author Topic:   Problems with Chromosomal Evolution - From Circular to Linear
Ooook!
Member (Idle past 5815 days)
Posts: 340
From: London, UK
Joined: 09-29-2003


Message 46 of 58 (137589)
08-28-2004 5:42 AM
Reply to: Message 39 by RAZD
08-27-2004 10:40 AM


Re: more thoughts to ponder.
I realise that it does nothing to really tackle the main point of the OP, but I do think it changes the nature of the challenge slightly. If the nucleus evolved from a parasitic or symbiotic organism that had a linear chromosome (in other words never made the transition to circular) then the chain of events stops being:
Linear => Circular => Linear (which seems like a wierd way of going about things)
to
Linear => Circular and Linear
Parasitic organisms would get around the problem of chromosome stabilisation by replicating like mad and using the host to keep their genomes relatively small, whilst others developed circular chromsomes to become all-singing all-dancing biochemical factories. It removes the absolute requirement for telomeres to survive, and presents the possiblity that parts of the hosts genome could be co-opted by the parasitic DNA to stabilise the ends of the relatively unstable linear chromosome (I think this is what Loudmouth was saying).
As for what the abstract said about the chain of events, I think I could sum it up like this:
  • The virus (or similar parasite) has a mechanism to trick the host cell into engulfing it.
  • The parasite then gets 'stuck' inside the host cell and a sort of symbiosis exists with a circular genome knocking around in the cytosol and a proto-nucleus.
  • The mechanism for engulfing things would still be active and the ability to prey on smaller cells would reduce the need for the first eukaryotes to make a lot of nutrients themselves.
  • As the genes in the circular chromosome would be less needed it would be easy to imagine a situation where important genes are sequestered by the nucleus and the rest of the 'host' geneome is lost completely.
This cell-turned-predator idea would also explain the advent of mitochondria and chloroplasts (but that is Off-topic)
Concerning the new topic suggestion: I certainly like the idea of a thread entitled 'All men are parasites' (or similar), but I'm afraid I don't know too much about the evolution of sex so I might have to do a bit of digging or turn it into more of an enquiry type of topic - unless you want to have a shot at it of course.

This message is a reply to:
 Message 39 by RAZD, posted 08-27-2004 10:40 AM RAZD has replied

Replies to this message:
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RAZD
Member (Idle past 1404 days)
Posts: 20714
From: the other end of the sidewalk
Joined: 03-14-2004


Message 47 of 58 (137659)
08-28-2004 3:34 PM
Reply to: Message 46 by Ooook!
08-28-2004 5:42 AM


Re: more thoughts to ponder.
It may well be that the original linear system was very inefficient and subject to frequent breakdown. It may even have been a not-quite-life system of chemical reactions that sometimes succeeded.
The issue of mitochondria and chloroplasts also speaks to the actual mechanism if one theory can explain them and the linear chromosome concerns (that occam flashing blade thingy)
Men as parasites or viruses -- they inject DNA into the host and coopt their reproduction mechanism to make a copy .... heh

we are limited in our ability to understand
by our ability to understand
RebelAAmerican.Zen[Deist
{{{Buddha walks off laughing with joy}}}

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Peter
Member (Idle past 1478 days)
Posts: 2161
From: Cambridgeshire, UK.
Joined: 02-05-2002


Message 48 of 58 (138371)
08-31-2004 7:56 AM
Reply to: Message 13 by Wounded King
08-23-2004 11:26 AM


If there was some "organism" several steps back from
both, that branched over a number of change cycles
to result in both types of cell then the link between
the types would be further removed and less of a conundrum.
What makes prokaryotic cells more primitive, BTW?

This message is a reply to:
 Message 13 by Wounded King, posted 08-23-2004 11:26 AM Wounded King has replied

Replies to this message:
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Wounded King
Member
Posts: 4149
From: Cincinnati, Ohio, USA
Joined: 04-09-2003


Message 49 of 58 (138383)
08-31-2004 9:15 AM
Reply to: Message 48 by Peter
08-31-2004 7:56 AM


If there was some "organism" several steps back from
both, that branched over a number of change cycles
to result in both types of cell then the link between
the types would be further removed and less of a conundrum.
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.
What makes prokaryotic cells more primitive, BTW?
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

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 Message 48 by Peter, posted 08-31-2004 7:56 AM Peter has replied

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Peter
Member (Idle past 1478 days)
Posts: 2161
From: Cambridgeshire, UK.
Joined: 02-05-2002


Message 50 of 58 (138723)
09-01-2004 5:51 AM
Reply to: Message 49 by Wounded King
08-31-2004 9:15 AM


ther isn't much room for some in between sort of common ancestor.
I wasn't thinking of 'in-between' when I was thinking of common
ancestor, rather more like enabling the development of either --
which really isn't the same -- honest
Why do you think your scenario is any less of a 'conundrum'
I was thinking more scope for changes to become manifest in
smaller steps ... in reference to this DNA structure comment
someone raised.
the prokaryotes precede the eukaryotes by a couple of billion years
So by 'more primitive' you just meant older?

This message is a reply to:
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Replies to this message:
 Message 51 by Wounded King, posted 09-01-2004 8:19 AM Peter has replied

  
Wounded King
Member
Posts: 4149
From: Cincinnati, Ohio, USA
Joined: 04-09-2003


Message 51 of 58 (138729)
09-01-2004 8:19 AM
Reply to: Message 50 by Peter
09-01-2004 5:51 AM


So by 'more primitive' you just meant older?
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

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 Message 50 by Peter, posted 09-01-2004 5:51 AM Peter has replied

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Peter
Member (Idle past 1478 days)
Posts: 2161
From: Cambridgeshire, UK.
Joined: 02-05-2002


Message 52 of 58 (138738)
09-01-2004 9:16 AM
Reply to: Message 51 by Wounded King
09-01-2004 8:19 AM


That works for me

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jt
Member (Idle past 5596 days)
Posts: 239
From: Upper Portion, Left Coast, United States
Joined: 04-26-2004


Message 53 of 58 (151248)
10-20-2004 12:37 AM


I'm back (sort of)
Hey guys,
Sorry for taking so long to respond - I'm very busy with school (I'm taking calc 2, physics, and chemistry, in addition to tutoring part time in the math lab), and I probably won't have enough time to respond the posts in this thread until a big, long break. Actually, I don't have enough time to participate in any thread which requires research, which means pretty much none of the science threads. (Loudmouth, if you read this, I saw your HERVs thread - very well written, and that is one of the arguments that currently has me stumped. I want to learn more about it and discuss/debate it with you, and I will when I have the time)
Just wanted to let y'all know that I didn't bug off into outer space or anything.
JT
This message has been edited by JT, 10-19-2004 11:38 PM

Replies to this message:
 Message 54 by NosyNed, posted 10-20-2004 12:44 AM jt has replied
 Message 56 by pink sasquatch, posted 10-20-2004 4:10 PM jt has replied
 Message 58 by RAZD, posted 10-20-2004 11:48 PM jt has not replied

  
NosyNed
Member
Posts: 8996
From: Canada
Joined: 04-04-2003


Message 54 of 58 (151259)
10-20-2004 12:44 AM
Reply to: Message 53 by jt
10-20-2004 12:37 AM


Sort of???
You mean, gasp!!, you have a life??

This message is a reply to:
 Message 53 by jt, posted 10-20-2004 12:37 AM jt has replied

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jt
Member (Idle past 5596 days)
Posts: 239
From: Upper Portion, Left Coast, United States
Joined: 04-26-2004


Message 55 of 58 (151265)
10-20-2004 12:49 AM
Reply to: Message 54 by NosyNed
10-20-2004 12:44 AM


Re: Sort of???
Aside of here, yes. Aside of school, only a little.

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pink sasquatch
Member (Idle past 6022 days)
Posts: 1567
Joined: 06-10-2004


Message 56 of 58 (151420)
10-20-2004 4:10 PM
Reply to: Message 53 by jt
10-20-2004 12:37 AM


Re: I'm back (sort of)
Hey JT,
I just "back into town" myself - if you feel there are loose ends in this thread you still want to discuss, let me know...
Good luck on your course load - remember that physics is really just math, and chemistry is really just physics, and biology is really just chemistry - so you really only have to study calc and the rest will follow...
(please don't actually follow this as practical advice, though it was given to me by a professor once... and has some degree of truth to it...)
good luck

This message is a reply to:
 Message 53 by jt, posted 10-20-2004 12:37 AM jt has replied

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jt
Member (Idle past 5596 days)
Posts: 239
From: Upper Portion, Left Coast, United States
Joined: 04-26-2004


Message 57 of 58 (151477)
10-20-2004 11:16 PM
Reply to: Message 56 by pink sasquatch
10-20-2004 4:10 PM


Re: I'm back (sort of)
I just "back into town" myself - if you feel there are loose ends in this thread you still want to discuss, let me know...
I still want to discuss the potential for t-loops to have been the evolutionary bridge between circular and linear chromosomes. When I get the time I'll definitely be tying that up (hopefully by clearly emerging as victor - possibly by winding up the loser - of this debate).
Very good advice - almost.

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RAZD
Member (Idle past 1404 days)
Posts: 20714
From: the other end of the sidewalk
Joined: 03-14-2004


Message 58 of 58 (151496)
10-20-2004 11:48 PM
Reply to: Message 53 by jt
10-20-2004 12:37 AM


Re: I'm back (sort of)
welcome back. looking forward to more.

we are limited in our ability to understand
by our ability to understand
RebelAAmerican.Zen[Deist
{{{Buddha walks off laughing with joy}}}

This message is a reply to:
 Message 53 by jt, posted 10-20-2004 12:37 AM jt has not replied

  
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