Problems with Chromosomal Evolution - From Circular to Linear

Hey JT-Nice opening post, and definitely a point of worthy discussion I haven't seen mentioned in the forum before.One thing you have to consider when you think about the evolution of a biological process or structure, (in this case linear chromosomes), is the simplest form of that process, and not the process as it exists in a mammalian cell.In this case, linear chromosomes exist in some viruses and bacteria, without the complex telomere maintenance you describe above.In some cases, repeated and palindromic sequences at the end of these chromosomes fold into complex hairpin loop structures (they fold back on themselves and bind complementary sequence) to protect free strand ends. (Searching for "linear bacterial chromosome" at http://www.pubmed.org should give you lots of interesting abstracts to look at). Thus it appears that the sequence itself is sufficient to protect the end of a linear chromosome in some situations, without any protein involvement.In certain bacteria, the chromosomes are unstable/reversible, in that they commonly go from circular to linear and back again.(reference) While such instability is negative in one sense, it also serves as a mechanism to "accelerate" evolution, since it provides more opportunities for rearrangements and duplications.Also, the fact that many simple linear chromosomes use palindromic hairpin loops as simple telomeres supports a plausible course of evolution for the linear chromosome. The palindromic sequence could have arisen within the stability of the circular chromosome (perhaps from a small duplication event), allowing for potential hairpin loops to form. Subsequent breakage of the circular chromosome near such loops would result in a linear chromosome having a "telomere" before it was even linear...There are still many points that deserve to be discussed from your opening post, but complex telomere maintenance does not appear to be required for linear chromosomes.

hey JT-This is a good discussion and I want to continue it, but unfortunately I'm in the process of moving my household, and so won't be able to contribute in the next two weeks. I haven't had a chance to check out the sources you linked yet to give a proper rebuttal...Though a word of advice: Throughout this discussion and others like it, try to come up with the simplest form of the process rather than looking to add complexity. Unfortunately this often takes us into the realm of speculation, but often you can take that speculation and find evidence supporting it in the literature.As a simple (speculative) example, a transient increase in temperature should be sufficient to unravel hairpin loops - perhaps an unstable environment aided in replication of some structures.When I get back to the forum I'll check out the progress on this thread.

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