In message .com, Don
H3 writes
On Nov 12, 6:33 am, (Nick Maclaren) wrote:
In article ,
Stewart Robert Hinsley writes:
|
| Indeed. I am half-expecting someone to find an oddity among even
| the mammals one of these days.
|
| Does the existence of 5 pairs of sex chromosomes in the platypus
| qualify?

Yes, but we can then debate whether they are mammals! Now, there
is an excellent, long-running, academic debate :-)

| It seems about as weird as
| permanent translocation heterozygosity in some Onagraceae (classically
| in Oenothera section Oenothera) ...

I require notice of that term! I have found a page for students that
explains it, and will read it when I have time ....

Regards,
Nick Maclaren.

Don't sweat it. Humans have between 65 to 95 percent "unused" or
"junk" genes (depending on how you count.) However it turns out they
are anything but "junk", mainly providing "blueprints" for specific
immune-response(s) to human diseases which have been rampant, and may
be so again, or other tricks-of-the-trade-of-staying-alive in a
hostile environment. I fully expect other animals and plants and fish
and what-have-you's to have similar tricksy information stashed in
_their_ "junk" gene pattern or pool. (Which is really the same thing:
if there is an epidemic, the "pattern" of one surviving individual may
permeate the pool.) It doesn't have to make sense to us for it to work.

In the molecular biology sense of gene humans don't have 65% to 95%
unused/junk genes - 0% would be more like it, a few percent if you
include pseudogenes.

Apart from protein coding genes, humans have stretches of DNA coding for
various sorts of RNA (ribosomal, transfer, spliceosomal, ...), stretches
which have regulatory functions and stretches which have structural
functions (e.g. telomeres). They also have a lot of DNA which is not
conserved (which is prima facie evidence for a lack of sequence specific
function), much of which is also repetitive, and identifiable as the
remains of retroviruses and transposons.

The amount of non-coding DNA varies greatly between taxa - this is known
as the C-value paradox. Humans lie in the middle - they have much more
than fugu, or thale cress, but much less than amoebas, salamanders or
ferns. We lack an explanation of the causes of this variation - for
example the Australian cottons have three times as much DNA as the
American diploid cottons - but some people argue for a bulk function
related to the regulation of the size of the cell and nucleus.
--
Stewart Robert Hinsley