Re: Fw: Most popular/common dinosaur misconceptions

[Roberto Takata <rmtakata@gmail.com>]

On 8/21/06, David Marjanovic <david.marjanovic@gmx.at> wrote:
> > Right, but even in vertebrates there are documented gene transfer events:
> > Numerous examples of mitochondrial pseudogenes have been documented
>
> This is exactly my point: if you put a mitochondrial gene into the nucleus
> (in a vertebrate), it does not work.

As I said elsewhere, it's just a question of either wait a minor,
though lucky, point mutation or transfer genes that do not use that
codon. In vertebrates its a bit more complicated because most nuclear
genes are under a very complex gene expression control system. And
remember that most of proteome present in the mitochondria are of
nuclear origin, which could imply a early gene transfer from
mitochondria (or the original endossymbiont) to nucleus.

> The other way around: the fact that the "universal" code is almost
> universal, and that all others can easily be derived from it, is evidence
> that the "universal" code is a synapomorphy of all life -- that life as we
> know it is, in other words, monophyletic.

No one is saying that the life forms that we know today are not
monophyletic. What is proposed is the possibility that the cenancestor
or its ancestral form could be originated by independently originated
genetic systems merging into a single biological entity.

The universal genetic code could either arise earlier - to do
reiterated interaction among molecular biota components - or could
arise later - in a progressive adjusting in the new formed life
system.

How could genetic system with different genetic code be compatible?
First, it could be the case that the translation system was not so
specific or so reliable. Recall the wobble hypothesis of codon origin.
And, on the other hand, termination codon is not a yes or no codon,
but a probabilistic codon - which depend somewhat of the genetic
context (the flanking sequences).

So if the universal genetic code arose later, it not even necessary
that all the nucleotides types used was the same.

As I said former, it a just-so-history. But maybe it could be
developed in a testable hypothesis someday.

[]s,

Roberto Takata