Re: Cell DNA versus body DNA quantity?

On Feb 25, 4:40 am, Vend <ven...@xxxxxxxxxxx> wrote:
On 24 Feb, 22:58, Ernest Major <{$t...@xxxxxxxxxxxxxxxxx> wrote:





In message
<3d9e9264-4bf6-4a4e-ba52-16d8f0465...@xxxxxxxxxxxxxxxxxxxxxxxxxxxx>,
Vend <ven...@xxxxxxxxxxx> writes

On 24 Feb, 14:01, Ron O <rokim...@xxxxxxx> wrote:
On Feb 24, 2:57 am, topmind <topm...@xxxxxxxxxxxxxxxx> wrote:

I'm curious about something that maybe a specialist here can answer.
What percentage of animal DNA is devoted to cell-level issues versus
body-level (super-cellular) issues? I realize there is some overlap,
but a rough estimate would still be satisfying.

It may help answer the question about why it has seemed to take a
relatively long time in Earth's history for multicellular life to form
and thrive. Cells may have needed to be sufficiently complex and
flexible before multicellular life was competitive.

Thanks

-T-

Sorry for the double post, I hit the wrong button.

There is considerable overlap.  You also have to consider that most of
the genome seems to just take up space, so we might just consider
known genes.  We will miss a fraction of noncoding DNA that is
involved in gene regulation for multicellular purposes.  Prokaryotes
that don't do much more than form colonies and biofilms have on the
order of 1000 genes.  Simple eukaryotes like yeast may not form
complex multicellular structures, but may have an order of magnitude
more genes (around 10,000), related fungi may form fruiting bodies and
still only have around 10,000 genes.  Infact humans still have the
same order of magnitude number of genes (around 30,000).

So if there is some kind of break point it occurred at around an order
of magnitude more genes that your usual bacterium needs to be about
the most successful lifeform on the planet.

There were probably enough genes to get the job done long before the
means to get them to all work together to produce a multicellular
organism evolved.

Ron Okimoto

How long did it take for multicellular life to appear after eukaryotes
appeared?

The uncertainties on the appearance of eukaryotes and multicellular life
are sufficiently large that we can't give a meaningful answer to that
question; on the one hand Cavalier-Smith dates eukaryotes at 800m years,
but on the other hand multicellular life is found at over 1,000m years
(Bangiomorpha). (Cavalier-Smith gets round that by interpreting
Bangiomorpha as a colonial bacterium.)

Perhaps it was a multicellular prokaryote?

Anyway, if (eukaryotic) multicellular life appeared shortly after
eukaryotes, could it be that all the mechanisms needed by
multicellularity were by large already present in unicellular
eukaryotes with other functions?

Eukaryotes have the advantage that they can keep track of more DNA in
an accurate fashion. Mitosis had to evolve and eventually meiosis.
Once eukaryotes could segregate multiple chromosomes accurately into
daughter cells there would have been a lot more slop in terms of how
much DNA you could keep around. More copies of any gene, more chances
to alter sequence and discover new functions.

I don't know how long this process would have taken. I'm sure that
someone has probably tried to infer the time of origin of the
mitochondria using molecular data, but I don't know what that estimate
is. You can't really use mitochondrial genomic sequence, you have to
try to use the genes transferred to the nucleus, but not all
eukaryotes transferred the genes at the same time. Some have retained
quite a few. That was also a key event when some early eukaryote
swallowed a purple sulfer bacterium and kept it as a pet. The
molecular estimates for metazoan origins (not including plants) have
error bars exceeding 1000 million (1 billion) years ago. Ayala had
some paper that indicated that over estimates for the age was expected
because you obviously have a threshold of zero but the amount of
change doesn't have that limit. It does have some limit because you
can start getting reversions double and triple hits that you can't
detect etc. I'm not enough of a math cruncher to figure out if he has
an argument. Taking the data at face value metazoan animals may have
evolved over a billion years ago.

Eukaryotes may have existed for a billion years before that, but I
don't know how much better than guessing that estimate is.

Ron Okimoto

There was some discovery hyped about finding evidence for eukaryotes
over 2 billion years old. They weren't looking at micro fossils so
much as the chemical residue left behind by the fossil colonies.
Beats me if they are going to get definitive answers that way.

Ron Okimoto




--
alias Ernest Major

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