Monday, August 29, 2005

Take out the trash

Question for the world, because I'm too lazy to google for it. Is the amount of "junk" DNA increasing, decreasing, or remaining constant?


Blogger Noumenon said...

I don't see how it can increase without steadily losing information, but it sure seems like there's a lot of duplication and stuff going on that would make it increase. Example:

right in the middle of it is a distinctive sequence of DNA that belongs to a sort that geneticists understand quite well, called an Alu element.

Alu elements get copied by our cells and those copies get inserted all over our genomes. Scientists can watch the process up close by putting molecular tags on Alu elements in a colony of cells, and then watching it spread over time. In the real world, a fertilized egg may wind up with a new Alu element, which then gets spread to every cell in the baby's body. Out of every 200 births, one child is born with a new Alu element. Sometimes they wind up wedged in the middle of a gene, disrupting its ability to make a protein. In some cases, this leads to a disease. More often, though, the new Alu element ends up somewhere in the genome where it doesn't do much harm. As a result, Alu elements piled up in the ancestors of living humans. The human genome has 1.2 million Alu elements, making up about 10% of its entire sequence of DNA.

Unless all of the Alu elements overwrote junk DNA, they must have replaced a few useful genes (maybe the ones for grasping toes).

2:04 PM  
Blogger Octavo Dia said...

The thought that prompted this post was a purely mechanical one, a concern about the direction of the nature of the universe. Evolution produces ever-increasing order, as useless and harmful things, such as junk DNA, are weeded out. Creationism posits entropy, so one would expect things to be getting worse. Neither theory would seem to fit, if things were remaining stable.

8:54 PM  
Blogger Noumenon said...

Evolution produces ever-increasing order, as useless and harmful things, such as junk DNA, are weeded out.

Natural selection's not directed toward more order necessarily, nor toward weeding out the useless and harmful. Whatever reproduces gets preserved, whether it's useless but good-at-replicating DNA or big wasteful peacock tails. Anyway, junk DNA is not well enough understood, it may have a function such as being a buffer for copying mistakes or it may just be not wasteful enough to provide selection pressure against it.

2:39 AM  

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