Is Human DNA as good as it gets?

Hi Mespo I suspect that there would be evolutionary pressure to limit the size of the genome where replication rate is highly selected. This could be the case in the gamete-producing cells of many organisms, and of course in the case of many pathogenic microorganisms.Such organisms do seem to have more "streamlined" genomes than human beings. "Bloated" DNA (i.e. introns, repetitive elements) are found less commonly in prokaryotes than eukaryotes. Part of the reason is probably due to the strength of selection on different populations. Populations of bacteria contain huge numbers of individuals, therefore selection is stronger because genetic drift does not play such an important role in determining the frequency of stretches of useless/bloated DNA. Populations of chimpanzees, on the other hand, are relatively tiny. Selection simply isn't strong enough to overpower the drift that naturally fixes gene bloat in the genome.in edit:
A key article for anybody interested in the evolution of genome complexity is The origins of genome complexity by Michael Lynch. You can get it free online in pdf form by doing a google search.Here's the abstract:

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Complete genomic sequences from diverse phylogenetic lineages reveal notable increases in genome complexity from prokaryotes to multicellular eukaryotes. The changes include gradual increases in gene number, resulting from the retention of duplicate genes, and more abrupt increases in the abundance of spliceosomal introns and mobile genetic elements. We argue that many of these modifications emerged passively in response to the long-term population-size reductions that accompanied increases in organism size. According to this model, much of the restructuring of eukaryotic genomes was initiated by nonadaptive processes, and this in turn provided novel substrates for the secondary evolution of phenotypic complexity by natural selection. The enormous long-term effective population sizes of prokaryotes may impose a substantial barrier to the evolution of complex genomes and morphologies.

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MickThis message has been edited by mick, 01-19-2006 04:13 PMThis message has been edited by mick, 01-19-2006 05:41 PM