Posted: May 20, 2014 4:40 pm
Rumraket wrote:DavidMcC wrote:Look, I didn't invent this stuff - it was part of my "Basic Bio" course by my employer, which was active in the field of biotechnology (involving DNA amplification on electronic chips).
So, you two don't accept that portions of a chromosome untwist ("fluff up") during gene expression, to allow enzymes to access the gene?
Of course that is accepted, this is common knowledge. This is not what has been in contention here.
Perhaps you should tell that to GfL, because he rejected it from me, claiming that it was only the "genic DNA" itself that was fluffing up.
DavidMcC wrote:The theory was that multicellular animals exploit the extra protection of genes from enzymes, which are large molecules, except during expression.
You don't need large swathes of neutrally evolving DNA to get the protective effect of chromatin packaging. Simply making genes wrap into the chromatin complex will ensure that protection.
OK, I'll take your word for that. At least you're keeping the thread rational.
The primary protection against accidental transcription is transcription factor binding site size. They're usually about 10 bases long, which can be shown probabilistically to be more than enough to ensure any two loci are extremely unlikely to evolve the exact same binding site.DavidMcC wrote:Rumraket wrote:We don't have to engage in this kind of ad-hoc, adaptationist rationalization. A lot of evolution is neutral and random, not everything has a selective purpose or advantage. We don't have to postulate that it does to explain it's existence or to understand it's origin and evolutionary history.
That was not my argument. I was taught that a major difference between prokaryotes and eukaryotes involved the latter having to keep most genes in any one cell completely silent all of the time, otherwise the wrong proteins and RNAs might be made in that cell, which could be fatal. That was part of the rationale given.
And as explained, chromatin packaging and transcription factor binding specificity itself ensures that, junk DNA or not. Again, look at the genome size variation! It would seem strange to imagine one species of fish needing 670 times as much protective junk than another. Or that between two virtually identical onions, one would maintain a genome five times greater than the other for that purpose.
No, it's simply junk being generated at higher rate than purifying selection can get rid of it. What you're doing is engaging in an ad-hoc adaptationist rationalization to explain the existence of large swathes of neutrally evolving DNA.
OK. I guess that there is very little selection against a very large genome, because it is only an issue during mitosis and meiosis, which is only occasional.