"Rob Halgren" wrote in message
...
Pat Brennan wrote:

Hi Joanna,

If you look at a plant's DNA only a small percent will actually be part
of a
gene and thus only a small percent is used in the coding for protein. If
you
look at a chromosome (a DNA strand) it looks something like:

. . . "tr a s h" . precursor . gene . " t r a s h" . precursor .
gene. . . .



Actually, in plants it looks more like this:
"trash".precursor.part1ofgene.junk.part2ofgene.jun k.part3ofgene.junk".
There is a whole lot of nothin' that breaks up the actual coding parts
of a lot of genes. Those are called introns, and I don't know that
anybody knows what they are for, either. Bacteria don't have them and
they get along just fine.

It has been more than ten years since I last discussed this with a
specialist in the genetics of animal development. At that time at least, it
was believed that the suite of introns used to form a gene varies through
development, so, for example, the actual composition of your hemoglobin
right now is different from what it was when you were a kid, and will be
different again when you're an ol' fossil like me. So, according to what
she told me, what counts as an intron or exon (what some refer to as junk)
will depend on age as well as the gene in question. Alas, she didn't have
answers for many of my questions, like "How exactly does the selection of
introns vs exons happen?" or "How is the gene constructed from the introns
once the introns have been made?" or "Is there any intermingling of introns
from different genes (e.g. is it possible to have an intron from one gene in
between the introns of some other gene); if so, how does the cell know which
introns are part of a given gene? or "How is the correct sequence of
introns in the gene stored and later recovered for use?" or "Does all this
happen in the nucleus?" or "How does the mechanism in a given nucleus know
what the age of the organism is in order to know which introns to use at any
given time?" or "Do the proteins within a chromosome have a role in any of
this, and if so, what?" Do you know if any progress has been made in
addressing any of these questions?

Cheers,

Ted