The reason why Eukaryotic Genome Tend to be Therefore Big
To say that the eukaryotes have large genomes, one should be comparing them to organisms with much smaller genomes, the prokaryotes. It is the analysis between these organisms which will give conclusive evidence why the eukaryotes have large genomes.
Immediately one jumps to the idea that the eukaryotes are more complex and therefore they need to have a bigger genome, where would inevitably produce more genes. This really is obviously true, though the complexity of the genome doesn’t directly match an increase in genome size. Wheat features a far larger genome than ours however, you might hesitate to call them more complex. Therefore, there should be more subtle underlying explanations 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 is 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 make sure they are much, much bigger than in the prokaryotes. The gene number difference in eukaryotes is all about 10 fold whereas the bottom pair number could be 1000 fold bigger. The question therefore lies within the introns of the eukaryotes. Why are there so many introns in the eukaryotic genome; giving rise to its ‘large size’?
Because the eukaryotes evolved from the prokaryotes one must elucidate the purpose of the introns in the eukaryotes as, say a stream (against transposons, mutation etc). גנום However, this could also be construed to have the same equally beneficial properties in prokaryotes. A much better approach is always to analyse the vitality output. Prokaryotes use 25% of these energy production in DNA copying and maintenance (the other 75% being that of protein production). Therefore, any upsurge in size of the DNA in prokaryotes would be too costly for the organisms to steadfastly keep up and replicate and thus the DNA is stripped down seriously to a very gene rich molecule. Eukaryotes are profligate in pouring energy to their genomes (due with their greater energy production capacity as an immediate consequence of getting specific organelles devoted to the purpose) and as a result they are able to afford to be so disgracefully inefficient and allow accumulation of introns.
Another and probably the main consequence of being able to pour large levels of energy into the genome is that eukaryotes can allow gene duplication events, which produce proteins that differ very slightly. Not only 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.