care to respond to a bit more than the last sentence, Bertv?
Bertvan@aol.com
Sat, 20 Nov 1999 17:34:07 EST Huxter:
It seems then that Denton is behind the times. 'Junk' DNA is used more as a
catch-all term for non-protein coding DNA. It is known - and has been for a
long time - that 'junk' DNA does (in some cases) have 'a' function. It is
also known that these functions are not nearly as dependant upon
conservation
of sequence as is the coding of protein for instance. Some have attempted
to
'up-play' the role of 'junk' DNA, claiming what you essentailly have (via
Denton), that there is function there, and therefore the sequence patterns
we
see are due to this. Some of those functions are spindle fiber formation,
chromosome structure, etc. According to 'Molecular Biology of the Cell, 3rd
Ed.', spindle fibers bind to kinetochores, which assemble at centromeres,
which have a specific sequence. The one mentioned is only 117 bases long. As
for chromosome structure and such, some intergenic DNA may very well have
'A'
function, but since it can accumulate so much obvious change, it stands to
reason that 1)these functions, if altered by sequence
change, are not necessary and/or 2)the function these regions have are not
affected by mutation. Also according to 'MBotC', replication origins in
eukaryotes occur every 30,000 to 300,000 nucleotides. It also mentions that
polymerases attach to the 'outside' of the double helix, or the
sugar-phosphate backbone, not necessarily a specific nucleotide sequence.
Moreover, many of the functional sequences in 'junk' DNA have a large degree
of degeneracy, so specific sequences are not necessarily required anyway.
Bert:
Since nothing else in living organisms has turned out to be "junk", I'm
inclined to
agree with Denton. Perhaps we will be able to answer lots of questions
when
we discover what function this "junk" performs.
Huxter:
Perhaps. Perhaps Denton should be a bit more well read rather than relying
on his anti-Darwinian feelings.
Bertvan:
Hi Huster;
I' m not sure what you want me to respond to. Apparently you have listed
some known functions of "junk" DNA. Are you suggesting no others will be
found? Or maybe you want me to comment on your declaration that Denton isn't
"well read"?
By the way have you any comment on Maynard Smith's reported comment in a new
book that,
"Darwin's theory of evolution by natural selection cannot alone
account for it; that theory predicts only that organisms will get better
at surviving and reproducing in their current environment, not that they
will become more complex. "
But then maybe he's not very "well read"?
Bertvan