The key reason why Eukaryotic Genome Will be Hence Massive

To state that the eukaryotes have large genomes, one must be comparing them to organisms with much smaller genomes, the prokaryotes. It is the analysis between these organisms which will give conclusive evidence as to the reasons the eukaryotes have large genomes.

Immediately one jumps to the indisputable fact that the eukaryotes tend to be more complex and therefore they need to have a much larger genome, where would inevitably produce more genes. That is obviously true, however the complexity of the genome doesn’t directly correspond to a rise in genome size. Wheat includes a far larger genome than ours however, one would hesitate to call them more complex. Therefore, there has to be more subtle underlying reasons why the eukaryotes have such large genomes.

Transposable elements increase the size of genomes by copying and inserting into different parts of the genome. However, transposable elements also occur in the prokaryotes and the affect of the transposons on eukaryotes in increasing how big the genome might be negligible. One reasons why the affect of transposons isn’t always detrimental to the organism is due to the introns present in a eukaryote. The gene rich DNA of the prokaryotes is in sharp contrast to genes scattered around eukaryotic genomes. The introns in the eukaryotic genome cause them to become much, much larger than in the prokaryotes. The gene number difference in eukaryotes is approximately जीनोम 10 fold whereas the base pair number can be 1000 fold bigger. The question therefore lies within the introns of the eukaryotes. Why is there so many introns in the eukaryotic genome; giving rise to its ‘large size’?

As the eukaryotes evolved from the prokaryotes one must elucidate the objective of the introns in the eukaryotes as, say a buffer (against transposons, mutation etc). However, this may be construed to really have the same equally beneficial properties in prokaryotes. A much better approach would be to analyse the power output. Prokaryotes use 25% of the energy production in DNA copying and maintenance (the other 75% being that of protein production). Therefore, any escalation in size of the DNA in prokaryotes could be too costly for the organisms to keep and replicate and thus the DNA is stripped down seriously to a very gene rich molecule. Eukaryotes are profligate in pouring energy into their genomes (due for their greater energy production capacity as a primary consequence of having specific organelles devoted to this purpose) and consequently they are able to be so disgracefully inefficient and allow accumulation of introns.

Another and probably the most crucial consequence of being able to pour large amounts of energy in to the genome is that eukaryotes can allow gene duplication events, which produce proteins that differ very slightly. Not just this, but in plants especially, entire duplication of genomes and addition of different divergent genomes are commonplace within that kingdom. Giving these organisms such huge genomes.

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