Friday, 30 March 2007

Secrets of DNA, Ted style...

Here's a little snippet I managed to pick up recently from a bunch of readign I've been doing:

I wouldn't have been doing the reading if evolution and selection worked as we are taught in classrooms. No this is not a creationist rant, rather the opposite. It's a "well shit that's clever!" kind of a look at how selection works.

For example, most so-called "mutations" are already there in the proteins and stuff, but they don't actually get allowed by the genesis processes unless there's some environmental variation that shuts down one of the normal processes and allows that variant to express instead. That means that a frog egg in a warmer pond will shut down some processes and allow others to take place, resulting in a generation where a higher percentage of the tadpoles will be more warm-adapted.

It's a clever thing, and the book I'm reading talks for whole chapters about how the DNA sequencing has working DNA and junk DNA and hints that the junk DNA may be an important "spacer" to place working DNA at the right point in the overall genome, and the book's author seems content with the fact that all those complex rules about what DNA is to be used for what, at what particular point of the process, that they miss the one point that stresses me out more than any other.

We have about 4,000 working DNA sequences and 100,000 proteins. That means that one piece of DNA codes about 25 proteins, not one to one as originally thought. Some of those proteins may well be being constructed as a result of other processes resulting from a protein that the DNA did code for, so maybe one DNA sequence can code for 12 different proteins, and this all depends on how far it is spaced by "junk" DNA from some other important DNA sequences or something.

That's a clever way to re-use DNA sequences based on their positions relative to one another or whatever. The rules that govern how each DNA sequence is used seem thus to be exceedingly complex. And I wonder how many biologists are working on the same question which I have:

Never mind how clever those rules are and how well they adapt life to the environment - how did those rules get created in the first place? If we can find out how such an appraently complex and very specific set of rules could have evolved to code the DNA, we would have a much clearer understanding of how to truly decode DNA...

Addendum: Reading further in the book, got to a piece about how one DNA sequence is a complete virus genome. The authors (Terry Pratchett, Ian Stewart, Jack Cohen) again say something thats both very deep and very shallow of them at the same time. You see, the retrovirus sequence prevents the mother's immune system from rejecting the foetus. According to Pratchett Stewart & Cohen, Messrs, "At some stage during mammalian evolution, this defence system was stolen from the viruses and used to stop the female placenta resposnding to the antigens that reveal the foreign nature of the fetus's (sic) father."

Good Messrs, this begs the simple question: What stopped the mother's immune system attacking the foetus before the retrovirus genome was adopted? Which came first, the retrovirus adoption or the foetus rejection? If it was the former, then why did the mammalian genome adopt a virus genome when there was still no foetus to give it a useful function?

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