At 08:38 PM 12/27/2012, David Roberson wrote:
It is funny when I hear of "junk DNA" as described by the genetics
experts. Why choose to call something unknown as junk instead of
just admitting that it is not understood? Reminds me of the old
theory about the amount of one's brain that is being used. I just
wish people would lay out the facts that they know and not judge the
unknowns. I guess some would call LENR junk physics!
"Junk DNA" refers to noncoding DNA. "Noncoding" means that the DNA is
not expressed as a protein. Noncoding DNA presumably sends no
messages, it's inactive. It may not be entirely so.
http://en.wikipedia.org/wiki/Noncoding_DNA deals with the complexity of it.
When I used the term "junk DNA," I was referring to what the article
calls "pseudogenes."
When it's said that much or most human DNA is noncoding, the article
says 98%. Some organisms have very little noncoding DNA, as 2% for
some bacteria. "Noncoding" is not a synonym for unknown function,
it's very specific. The sequences are not transcribed to proteins.
Some noncoding DNA is known to have functions, I mentioned telomeres
in another post. There are sequences that aid in transcription of
neighboring sequences.
The article has:
The Encyclopedia of DNA Elements
(<http://en.wikipedia.org/wiki/ENCODE>ENCODE)
project<http://en.wikipedia.org/wiki/Noncoding_DNA#cite_note-Nature489p57-1>[1]
reported in September 2012 that over 80% of DNA in the
<http://en.wikipedia.org/wiki/Human_genome>human genome "serves some
purpose, biochemically
speaking".<http://en.wikipedia.org/wiki/Noncoding_DNA#cite_note-pennisi-2>[2]
And here is where having some idea of how Wikipedia works can be
helfpul. This is very recent. The ENCODE project made that
announcement about three months ago and there hasn't been time for
much response.
http://en.wikipedia.org/w/index.php?title=Noncoding_DNA&diff=518424872&oldid=514740309
is an edit by an anonymous editor that removed a comment that the
claim has been criticized. The claim was unsourced and was properly
removed, but ... what *has* been the response?
There is some decent discussion at
http://en.wikipedia.org/w/index.php?title=Talk:Noncoding_DNA&oldid=517850643#Misinterpretation_of_ENCODE.3F
The issue appears to be that much of the 98% noncoding DNA is, in
fact, transcribed, into RNA, which then serves certain functions. The
project still seems to leave about 20% of the genome as
nonfunctional. As pointed out in the discussion, noncoding DNA can
sometimes be reactivated under selection pressure. That requires a
mutation, but only one, perhaps. So the noncoding DNA might be a
junkyard, and a junkyard can be very useful!
One of the key issues about pseudogenes is that, being nonfunctional,
being, sometimes,
<http://en.wikipedia.org/wiki/Endogenous_retrovirus>Endogenous
retroviruses that were deactivated after being inserted into human
cells, having no human biological function, they are not under
selection pressure, which causes the retained mutation rate to be
much higher for these sequences, it's a raw measure of raw mutation
rates, not being selected, since mutations in those regions are
almost always neither of harm nor of benefit. And so these can be
used to study evolutionary time.
