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This question already has an answer here:

Why did Eukaryotes evolve to have linear DNA and not circular like Prokaryotes? What are the pros and/or cons?

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marked as duplicate by fileunderwater, Bez, HDE 226868, p.s.w.g, March Ho Feb 21 '15 at 17:59

This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.

  • $\begingroup$ Some prokaryotes have linear DNA too.. $\endgroup$ – WYSIWYG Feb 21 '15 at 7:18
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This question has been asked before: Is there an advantage to linear chromosomes?

Firstly, I should state that the generalisation that ALL prokaryotes have circular genomes is incorrect. A growing number of prokaryotes have been discovered which have linear chromosomes, such as Borrelia burgdorferi ,which causes Lyme disease, members of the Streptomyces family and Agrobacterium tumafaciens, which has both a circular and a linear chromosome.

Anyway, on to the question being asked:

Generally, my feeling is that large circular chromosomes would have much greater supercoiling and related torsional problems, making it difficult to unwind them for transcription, replication or repair. This limitation on physical size limits the amount of genetic information that can be carried in a single chromosome, thereby limiting complexity of the organism.

You could increase the number of circular chromosomes to compensate for their lack of size, but again, you end up having a physical limitation (size of the nucleus or size of the cell for anuclear organisms) on how many chromosomes you can pack into the cell.

Linear chromosomes are just a more efficient shape when it comes to larger sizes.

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Here are a few good references to dig further, if you're interested:

  1. A new beginning with new ends: linearisation of circular chromosomes during bacterial evolution. Pubmed: http://www.ncbi.nlm.nih.gov/pubmed/10802162

  2. Why do we have linear chromosomes? A matter of Adam and Eve. Pubmed: http://www.ncbi.nlm.nih.gov/pubmed/10422538 -- Proposes that meiosis was the driver for linear chromosomes.

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  • $\begingroup$ I concur with your argument but it would be great if you can add some references. $\endgroup$ – WYSIWYG Feb 21 '15 at 7:38
  • $\begingroup$ Added, as requested. Here's a really interesting experiment where they linearised the normally circular E. coli genome and studied the cells: ncbi.nlm.nih.gov/pubmed/?term=PMC1796773 $\endgroup$ – Cantona's Collar Feb 21 '15 at 7:50

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