baez@x.ucr.edu (john baez) (04/12/90)
In article <1990Apr12.020601.28357@msuinfo.cl.msu.edu> riordanmr@clvax1.cl.msu.edu writes: >Plasmids are rather common in >fungi which are eukaryotes, particularily in the mitochondria which are >themselves believed to be prokaryotic in nature. In a recent posting I may have been under the temporary delusion that plasmids sneak into human cells - normally I know better (though now I wonder: how much evidence is there that plasmids don't sneak into, say, vertebrate cells - and how much better "protected" are they than fungal cells?) Okay, on to PALEOGENETICS. This seems really neat to me. Being in the math department here at UCR, I only hear about what they're doing in the biology department when it makes the LA Times :-(. Today they say that plant geneticist Michael T. Clegg has used polymerase chain reaction to amplify some DNA from a magnolia leaf that's 20 million years old!! The oldest material previously decoded was only 7000 years old. "The magnolia leaf the researchers used was not a conventional fossil, such as those found in most fossil deposits. Rather, it was a so-called "plant leaf compression" containing almost all of the original leaf tissue[....] The fossils were preserved at the bottom of a lake that formed when volcanic lava dammed a valley in the hilley region [the Clarkia cite in the western foothills of Idaho]. Leaves and other materials settled to the bottom, where the stagnant, deep water was devoid of oxygen. Sediments filled the lake over a period of 750 to 1000 years." "Once the amount of DNA had been amplified, Clegg and Golenberg used conventional techniques to identify the sequence[...] of the ancient leaf's gene that codes for a protein required for photosynthesis[....] the researchers found that evolution took place at the rate of one mutational event, or change in the DNA sequence, every million years." Do they mean 1 change *for the whole chromosome* per million years, or for that particular gene, or what????? One change per chromosome per million years seems awfully slow to me... From the sublime to the mundane: here's one of those dumb questions that festers until you come out and ask it. Every time I wash my lettuce, I wonder, if lettuce grows from the inside out (i.e. the outside leaves now were always on the outside), if I want to wash off pesticides isn't it enough to wash off the outside leaves? (As you can see, I'm lazy.)