afc at gnv.ifas.ufl.edu (Andrew Cockburn) writes:
>It is correct that most genomic DNA in higher eucaryotes is noncoding.
>However, the argument that most of this is repetitive is blatantly
>homocentric.
*Also, let's remember that a significant portion of human
repetitive DNA, namely the Alu repeats, code for the 7SL RNA that is a
component of signal recognition particle. Not all "complex" repetitive
DNA is retrotransposon or other selfish DNA, or "mysterious" in some way.
>In Drosophila and many other insects, a third or less of
>the DNA is repetitive.
*The readers of this thread would do well to review Britten &
Kohne's 1968 Science paper for the definition & initial methodology on
genomic DNA complexity measurements, as well as the long series of Cot
curve experiments by Britten & Davidson & their colleagues.
>What I would like to see is an explanation of how a small genome
>can evolve from a large genome full of repeats. I believe that this
>happens in insects fairly frequently. Allen Spradling suggested to me
>that this might be tied up with the mechanism of polytene
>chromosome formation, which involves deletion of repetitive DNA.
*Not being privy to the exchange you had with him, I don't know
what Allan had in mind. I wonder how the mechanisms at work in
underreplicating or eliminating portions of the genome in *somatic*
polytene tissues could bear on the behavior of *germline* chromosomes.
Please elaborate for us.
