Centromeres in Chromosomes in DB

[shvarz]

Well, I can actually see the point that Scientific American was trying to make, but the guy who wrote the post did not.  If DNA is artificially removed from the cell, then the cell is not "dead" right away.  It will surely be so in some time and once it dies no virus would be able to re-animate it.

Can you drive a car that has no engine?  No.  What if the car was running on a highway and suddenly something took the engine out.  Then you could (theoretically) jump in and "drive" it until it stops.  That's a pretty good analogy to what happens when a virus infects a cell with no DNA.

[Endy]

See your point.

Although the difference between viral and DB dna is currently nonexistant.
The only real limit on size(and complexity) is the sheer time constraints on viral creation.

Endy B)

[shvarz]

Coming back to centromeres:

Right now I don't see any reason to implement centromeres.  I mean "We can, but why?"  

Centromeres bring similar chromosomes together, allowing two important functions:
1. Homologous chromosomes can recombine
2. Sister chromatids are separated during division, allowing both daughter cells to have a complete set of chromosomes.

As far as I see it, we can do both with the "local homology" system that we already discussed.  It can be used first to find similar chromosomes (by simply starting from the beginning) and then later to allow recombination in homologous regions.

These two processes will allow "conserved structure" of a genome and at the same time will allow certain "fluidity" in this structure.  Chromosomes can be created, they can change length, they can swap large regions and so on...  All through recombination and chromosome division.

The only thing that is not possible with this system is breaking of a chromosome into two parts.  I don't even think it is that important, but if people want it, we can always add a new kind of "mutation".

Another downside to this system is that it is "imposed from above" - bots don't evolve it - it is just there for them to use.  But I think even the ability to use it in a meaningful way is already a challenge for evolution.  So I think it is a minor downside.