Problems with Chromosomal Evolution - From Circular to Linear

Nice topic. The only comments I have to add are:(1) That breaks in the circular chromosome would occur leading to repeated attempts at linear chromosome arrangements. These could just keep happening until a process co-evolves that allows it to survive.(2) It could be argued that the original replication system would have used a linear system (see discussion of RNA replication), and thus have developed a primitive solution to the end problem before finding the more stable circular system, and that this would have continued to be available when such breaks occured as in (1) above.Remember that you are dealing with differential survival rates and those that do it better faster have more replicating survivors.I look forward to the next post Thanks.This message has been edited by RAZD, 08-21-2004 12:10 AM

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

The above looks similar to my argument (2) ... but I'll wait for you to get to it. (reference http://EvC Forum: Problems with Chromosomal Evolution - From Circular to Linear)

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

well it doesn't cover argument (1) of mine - that circular chromosomes broke open regularly and eventually one survived, or the element of (2) that the first chromosome (proto-chromosome?) was linear, from which the circular evolved as a more stable form, and therefore whatever system the original form used would still be available when circular ones broke open.No hurry. I'm enjoying the read so far.

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

Immediately? Tomorrow? Next week? What is the time frame here? What kills it? There will always be some molecules available inside the cell that may be added to the end of the chromosome as it tries to close\repair itself ... what happens when one holds it together just enough ... Implausible is not impossible.Why does it have to be DNA? We are talking the first replicating cell system and the environment then was totally alien to what we live in, the chemical energy system was different. Latest thought is that RNA could have just as easily been the best replicator before DNA evolved from it, perhaps there was a simpler but less effective molecule before that. The LUCA project is trying to determine just how little\simple the replicating molecule needs to be.Why do you assume it stopped being needed? If circular chromosome breakage was common a stabilizing system could be maintained and even improved with time to hold things until circularity was re-established. Perhaps they are the molecules that first caused the circular chromosome to close, that becomes a repair molecule, that gets damaged while not needed but then employed in a new way ...... and a molecule that was needed from time to time could then be fatal to the ones that lose it and then break open.Certainly a linear molecule is simpler than a circular one, so evolution and probability would tend to favour the linear system first. A crude inaccurate system with a high degree of failure would still out compete pure chance combination of amino acids -- remember it does not have to be as good as the system today (in a different environment), it just needs to be good enough.and the issue of improbability has been addressed on other threads -- think of a lottery: highly improbable that any one specific ticket will win, highly probable that one of all the tickets will win ...
see http://EvC Forum: the old improbable probability problemand if it did "just happen" then the improbability is irrelevant.enjoy.

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

Hmmm a DNA viral mechanism could also hark back to a more primitive organism overshadowed by later evolved more complex cells. Certainly by the time we are talking about developing eukaryotes, life has been around for a while.This talks about the first predator engulfing others for raw materials, while the viral model is to enter the 'prey' and attack\co-opt from inside? This also leaves the original outershell as camoflage in case of colonies.Other papers have suggested a lot of DNA\RNA interchange between early cellular organisms. A form of group sex?These viral remnants would still have already developed the capping\telemere solution by this time as well. Thus this does not solve our OT problem.One thought this brings to the OT problem though is that dead and dying cells would be consumed by others, cells that had broken circular chromosomes could be incorporated, and in the process get combined with other remnants, one becoming a cap for another.interesting thoughts.Going off on a tangent I posit that a virus entering a cell is similar to a sperm entering an egg ... perhaps this mechanism is behind the evolution of sex (once a symbiotic relationship has become established)? The idea of males as viruses would, I'm sure, amuse many. Could be an interesting new topic?

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

has anyone tried to remove the end caps from straight chromosomes and see if a protection system evolves?are there molecules that cause circular chromosomes to open, and are they catalytic or do they combine in the process?

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

OK. We'll try to keep it down to a dull roar so theren won't be too much to cover.You may want to bookmark your last post on this topic so you can get back to it even if it has dissappeared from the radar?

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

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

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

welcome back. looking forward to more.

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