On the proportion of Nucleotides in the Genome and what it can tell us about Evolutio

As CS notes, it is a massive assumption to suggest that Natural Selection has not played an active part in forming this distribution.That aside there are other factors which affect these ratios. One major factor is the fact that methylated Cytosines, specifically 5-methylcytosine, can be readily converted to Thymine by de-amination. This is one of the most common single nucleotide substitutions observed. This alone could account for a large proportion of the discrepancy.TTFN,WK

You seem to be being obtuse. Your approach would also presumably predict that the frequency of use of all amino acids should also be equal and unaffected by natural selection.You can't uncouple the fact that functionality is determined by amino acid sequence form the DNA triplets that encode those amino acid sequences. If particular functional domains or structures are persistently coopted to form other proteins then that will affect the proportions of nucleotides dependent on the exact amino acid sequence involved. It is worth noting though that in vertebrates coding sequences actually have a higher GC content than the genomic background so Natural selection appears to be acting to maintain GC sequence that might otherwise be lost.TTFN,WKEdited by Wounded King, : No reason given.

I don't know other proportions off the top of my head. You can presumably find thes out for any organism which has had its genome sequenced, and there are probably rough estimates for many other species.I'll see if I can find out some more tomorrow, but bed calls for now. In the meantime doing a search for terms like 'GC content' on Entrez/pubmed could turn some interesting stuff up.Another important consideration is that a lot of the genome is made up of highly repetitive sequences, so the composition of those repeated elements could heavily influence the makeup of the whole genome.TTFN,WKEdited by Wounded King, : No reason given.Edited by Wounded King, : No reason given.

They certainly can, and there is some evidence that highly transcribed regions are more prone to mutation, but that is important principally in somatic mutations, in the germ line mutations which actually contribute to heritable variation this effect will be considerably reduced. It is by no means that case that mutations only happen during transcription, perhaps more important in evolutionary terms are meiosis and mitosis which similarly involves the unwinding of DNA to allow DNA synthesis enzymes to have access to single stranded DNA. You are basing your reasoning on a number of huge assumptions. Wow, that is the sort of argument that creationists always use as a strawman of what biology says. I don't think anyone familiar with modern biology really believes this. The majority of the genome is composed of non-coding DNA, but this isn't the same thing.Unless you specifically define 'Junk DNA' as DNA which is neutral in terms of selection, i.e. non-functional, then any of the commonly used meaning of the term show your statement to be wrong. There are a number of non-coding sequences in the genome that have been targets of selection. Many of these serve structural roles in stabilising the chromosome, see microsatellite DNA, Telomeres, Satellite DNA and probably othe as yet uncharacterised sets of sequences. There are also regulatory elements which are found to be embedde in intergenic regions which might previously have been discounted as 'Junk'.TTFN,WK

Do you think that these advancements arose from creationist research? What is the most recent paper you can find propounding Ohno's original formulation, I doubt you could find anything much more recent than the eighties. Certainly by the time I went to University in the 90s the roles of numerous non-coding regions were appreciated and taught in an evolutionary context, hardly maintaining a strawman of non-functional 'Junk' DNA.'Junk' DNA was one of those frequent instances where a scientist made some predictions based on an incomplete understanding of the system. Even with the new functional transcribed non-coding elements and long distance regulatory elements that we are aware of there is still plenty of microsatellite DNA and highly repetitive regions to perform the sort of non-functional functions, like spacing between genes or surrounding centromeric regions, that Ohno suggested 'Junk' DNA had. The main thing Ohno had wrong was thinking that 'Junk DNA' was principally derived from 'failed' genes, there are certainly many pseudogenes which may be degenerate gene duplicates but the larger proportion of 'Junk' DNA originates from transposons. Even these transposon originated sequences serve some regulatory functions occasionally.As you say Kimura and Haldane are another topic.TTFN,WK

That needs to be 5-methyl cytosine for it to really work. There are enzymes which specifically excise and replace uracil bases in the DNA. The repair system may still allow a few through though. 5-Methyl cytosine changes to thymine which can't be distinguished.Also uracil binds to adenine not thymine.TTFN,WK