Hey all,

 

I have been thinking about the evolutionary accumulation of introns. Firstly, they used to be referred to as "junk-DNA" but now we know that this is not exactly true. For example, intron splicing is responsible for the K+ channels in our ears that enable us to hear different frequencies. However, could they still have accumulated as junk and only later been shaped by natural selection for specific purporses? If they were once just junk, why are there no introns in prokaryotes? They seem as good DNA carries as eukaryotes. It seems logical to suppose that the advance transcription machinery in eukaryotes requires introns, while the prokaryotes do not. This once again leads to an evolutionary selection but this would have had to be a slow accumulation with selection at every step. What would be the benefit of carring extra DNA in your genome? It does not seem economical. Have there been any other roles, besides splicing, discovered for introns? Fascinating things, they are.

 

Thoughts please.

Introns are also have regulatory effects and supposed to stabilize essential domains. For higher eukaryotes the costs for additional DNA elements in form of introns is arguably not that high (when compared to the overall metabolite content of a given organism). This is not true for very small single-cell organisms (all prokaryotes for example). In these there is a selective pressure towards compact genomes (as here DNA replication can be one of the limiting factors of growth rates.