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

You'll find G-C figures easier to get hold of, probably, because they're the one's traditionally used. G-C %ages were long used as a means of classifying microbial species, so there's a lot out there about them. They're increasingly being replaced by more sophisticated phylogenies based on actual sequences.As others have noted your assumption that the %ages are not adaptive is simply false. A-T pairs have a double bond, G-C pairs have a triple bond; this means that A-T pairs are easier to seperate, and G-C are harder. So, for example, the origins of replication on genomes (of which there are many on eukaryotic chromosomes, and some archael chromosomes and one on bacterial and most archael chromosomes) have a very high proportion of A-T pairs because these can be easily seperated.Thermophillic bacteria have higher levels of G-C pairings that their mesophilic relatives (that is, bacteria adapted to higher temperatures have more of the triple bonding G-C pairs which is thought to aid DNA stability). However, among archaea (the true kings of high temperature living), this link between temperature and G-C content doesn't hold. Species such as Pyrolobus fumarii (which can survive at up to 113 ^oC and grows best at 106) use protein and enzyme chaperones to mphilic relA stability instead.Finally, there are also specific sequences that perform non-coding functions that can be higher or lower in the two - e.g. the TATA box which indicates gene starts.So, you see, the picture is much more complicated than a simple random variation between the letters.

The median modal number of times for a sequence of heads and tails to cross the zero line is 0, with all higher numbers occur with decreasing probibility.The reason for this is quite obvious if you think about it: because all future flips occur independently of those flips that have already happened, the chances are that there will not be a trend reversing any initial discrepency from zero.Edited by Mr Jack, : Added explainationEdited by Mr Jack, : Meant mode not median

Sorry, I meant mode. My bad. No, I'm not. More paths will not ever cross the zero line than any other particular number of crosses; what is more as the number of crosses increases, the number of paths that have that number of crosses decreases.

Nosy, it correct, I was discussing crossings, not meetings.And, as I said, I meant mode not median. Again, my bad.

Mean is an extremely poor choice for a situation such as this - especially when considering the infinite limit - because of the large value distortion effect, and the non-normal distribution of the probabilities.The most probable number of crosses is 0, followed by 1, followed by 2, followed by 3, etc.

But you've not crossed it unless the next toss is the same.HTH meets the zero line, it does not cross it
HTT meets and then crosses the zero line.Of the possible 3 toss sequences, then, HTT and THH cross the line once; the other six do not cross it at all.

After looking it up, I realise I have erred. In fact, the result I stated holds for a finite random walk, but it does not hold for an infinite random walk.

You're not humpty-dumpty, words don't mean what you choose them to mean. Touching and crossing are different concepts.

You used the wrong word. Funnily enough, since I'm not psychic I figured you meant the word you used.

You used the word wrongly. Crossing in maths means crossing, just like you'd expect.Man up and admit your error.

You've misunderstood my point. The differences in strength of bonding are themselves adaptive. Bacteria adapted to high temperature environments have more G-C bonds because this increases the stability of the DNA. Origins of replication have high levels of A-T bonds because these can be more easily seperated. This is true only of the Eukarya, in Archaea and Bacteria, the majority of their DNA is not junk.

Because of deamination (in which cytosine loses an amine group, and is converted to uracil which then binds to thymine rather than guanine during DNA replication) it sees quite probable that GC -> AT point mutations are more likely than AT -> GC point mutations.

Yes, sorry, binds to uracil, thus replacing the cytosine with thymine *sigh* And, yes, most such changes are caught, but not all. Which should provide a bias to the probability to GC->AT vs. AT->GC changes.