How and when did chromosomes first appear?

[mynah]

(True chromosomes of eukaryotes, that is, not DNA as such.)

Here is an interesting and plausible theory about the evolution of the nucleus:


Crucial Evolutionary Link Points To Origins Of Modern Cells

Does anyone know how much support it enjoys?

If the above is true, the nucleus may have appeared much earlier than true chromosomes, and many organelles, including mitochondria, could have evolved long before the switch from a prokaryotic to an eukaryotic genome took place.

[freeztar]

Originally Posted by mynah

(True chromosomes of eukaryotes, that is, not DNA as such.)

Here is an interesting and plausible theory about the evolution of the nucleus:


Crucial Evolutionary Link Points To Origins Of Modern Cells

Interesting article.

Does anyone know how much support it enjoys?

No. I tried to look this up without any luck. I did however find the lead author's academic page:
The Rockefeller University - Heads of Laboratories

If the above is true, the nucleus may have appeared much earlier than true chromosomes

I would hypothesize that the nucleus appeared before the chromosome since the nucleus helps package the chromosome. Though, this could be a bit of a "chicken or egg" argument.

many organelles, including mitochondria, could have evolved long before the switch from a prokaryotic to an eukaryotic genome took place.

Can you elaborate on why you believe this?

[mynah]

The membrane system described in the article would have allowed for the formation of vacuoles, lysosomes, transport systems and the outer membrane of the mitochondrion without the need - at least in a simple unicellular organism - for chromosomes as they are known today. Of course, that just means that true chromosomes could have evolved at a later stage rather than at the same time, not that they actually did so. (Hope this makes sense. It's 05:30 here and I've been working through the night...)

I do find the lack of information on the origin of eukayotic chromosomes rather strange. Surely there must be many researchers working on the subject?

[freeztar]

Originally Posted by mynah

The membrane system described in the article would have allowed for the formation of vacuoles, lysosomes, transport systems and the outer membrane of the mitochondrion without the need - at least in a simple unicellular organism - for chromosomes as they are known today. Of course, that just means that true chromosomes could have evolved at a later stage rather than at the same time, not that they actually did so. (Hope this makes sense. It's 05:30 here and I've been working through the night...)

That makes sense. I just wonder what would be the selective advantage of a prokaryotic cell developing such oraganelles. Perhaps there was no apparent advantage and it was random?

I do find the lack of information on the origin of eukayotic chromosomes rather strange. Surely there must be many researchers working on the subject?

Since research is largely driven by grants and such, it's not too surprising that there is not a lot of research on this subject (combined with the fact that, intuitively, it would seem very difficult to practically conduct such research). I'll do some searching to see if I can find more on this.

A quick search reveals this article, which may be quite pertinent to the topic:
Primitive Genetic Mechanisms and the Origin of Chromosomes

[Moontanman]

I think the idea that mitochondria, chloroplasts, flagella, and other organelles were micro organisms that merged with a cell, sometimes as predators and sometimes as food to eventually become part of the cell.

[freeztar]

Originally Posted by Moontanman

I think the idea that mitochondria, chloroplasts, flagella, and other organelles were micro organisms that merged with a cell, sometimes as predators and sometimes as food to eventually become part of the cell.

That's certainly a reasonable theory. I like the idea of an eventual mutual dependency from a host/parasite mutualistic relationship.

So what about the chromosome MTM?

[Moontanman]

Originally Posted by freeztar

That's certainly a reasonable theory. I like the idea of an eventual mutual dependency from a host/parasite mutualistic relationship.

So what about the chromosome MTM?

If indeed some of the internal parts of the eukaryote cell is the result of mutualism the smaller less obvious parts may be too. The idea that the first life (cell) was the result of many different chemical processes coming together in mutually beneficial relationship Can (I think) also explain the complexity of the eukaryote cell. The three i mentioned earlier are the most obvious but the more complex internal make up of the eukaryotes may also be the result of various less complex cells contributing parts of themselves in an almost Frankenstein way. At some point a cell learned to use parts of other cells as more than just food and incorporated these parts into it's self. The chromosomes could be a part of this process. Possibly to protect the "self" of the cell. Chromosomes were concentrated inside a membrane that was co opted from the parts of cells that come together to form the eukaryotes cell. I think of it in the same way the many different cells make up a complex organism and in a real way these cells are independent creatures. a eukaryote cell is a real colony of different simpler cells. some of these cells maintained more of their integrity than others but they all work together to make the eukaryotes cell. Possibly all the new genetic info and keeping track of this info from several different organisms may be why the chromosomes came about.