Re: Evolution of Separate Genders in Animals

On 6 Mar, 15:00, "Perplexed in Peoria" <jimmene...@xxxxxxxxxxxxx>
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On 6 Mar, 03:30, "Perplexed in Peoria" <jimmene...@xxxxxxxxxxxxx>
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On Mar 5, 8:45 pm, "Perplexed in Peoria" <jimmene...@xxxxxxxxxxxxx>
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On 5 Mar 2007 12:09:35 -0800, "hersheyh" <hershe...@xxxxxxxxx> wrote:

On Mar 5, 12:35 pm, "derdag" <der...@xxxxxxxxxxxxxxxxxxxx> wrote:
On Mar 5, 5:46 am, "SJAB1958" <balf...@xxxxxxxxxxx> wrote:

Can anyone help me out with a query? I know that the swapping of
genetic material between organisms arose before the formation of
separate genders, but did separate genders come before
hermaphrodites
or was it the other way round? Any website links that would help
here
would be greatly appreciated.

When evolution decided ...

"Evolution" does not 'decide' anything. That would be ignorant
anthorpomorphism. Unlike our dear Prez, evolution is not the
'decider' of anything. Local environmental conditions, OTOH, are the
the dumb, unintelligent decider between variants based on how well
those variants reproduce.
<snip>

When normal people say that evolution "decides" or "chooses", it is
simple anthropomorhic shorthand, a common practice among the
cognoscenti. When derdag says it, it is plain ignorance, not
specifically anthropomorphic ignorance.

And, lest derdag think we are picking on him, notice that he did
write: 'A couple of them had the same idea at the same time.' A couple
of what? A couple of species? No evidence that it would have been
at the same time. A couple of individuals? Individuals don't 'decide'
in any sense in the ToE.

How about suicide?

Well, OK. Or the decision to have a large family. Or the decision to
migrate. Individual decisions can influence the direction in which
population gene frequencies go. However, they cannot result in heritable
genetic mutations.

Well, OK. The decision to become a worker in a nuclear plant or an
airline pilot. But individuals in a population of asexual reproducers
don't 'decide' to reproduce sexually instead and pass that trait on to
their children. Which is what I think derdag was suggesting.- Hide quoted text -

- Show quoted text -

derdag did suggest that there was a problem at the time some and I
mean (one) cell underwent meosis instead of mitosis, needing a proper
(irreducibly complex) structure present for combining with another
haploid cell (and there must have been only (one other one) to become
a diploid cell. It could do it several times and there would still
only be one cell. God Bless you for putting up with this stupidity.
lol I realize that if this occured in a sex cell of a multicelled
organism, that the problem would be somewhat less complex in that
way. However, if that were the case we would need two organisms to
develope the lock and key mechanism and find eachother.

Lets just assume that the other poster is right and that mitosis
became meosis in a single celled organism. The other problems are
even more complex. (1+1) becomes (1) and (1); and then (1) and (1)
combine to become (1+1) again.

Man, that works out pretty sweet.

Meiosis is more complicated than you seem to think. It is not (1+1) becomes
(1) and (1). It is more like (1+1) becomes (1+1+1+1) which then becomes
some number between one and four of (1)s. Probably fusion - (1) and (1)
become (1+1) - was already a well developed behavior long before meiosis,
with its complex sequence of events got 'invented'. And it is also likely
that the nuclear aspects of this sexual dance were developed in a polynucleate
cell. Only later did the nuclear events become obligately linked to cytoplasmic
fission and fusion. IMO.

I agree with that last point. It is still difficult to imagine
systems intermediate between mitosis-only, and meiosis/fertilisation
plus mitosis.

I'm wondering whether mitosis is really the same process in the
haploid and diploid case. I.e are they both equally agnostic about
chromosome pairing by homology? (The relevance of that question is
that I'm wondering if originally only the haploid phase could
multiply, and that meiosis/fertilisation were originally an
indivisibly scripted sequence within a 'conjugation' of some sort.)

I think that is quite likely. Also that 'conjugation' was a response
to some kind of lack of raw materials or DNA damage. The original
purpose of recombination was DNA repair. But doing so results in
Holliday junctions half of the time, and half of the time resolving
them results in a crossing-over.

I think there is a level confusion here, but I'm not sure. I mean, I
know there are strand level repair mechanisms for transcription
errors,

I think you mean replication errors rather than transcription errors.

but are there helix level ones?

Yes.

I.e. can an irretrievably
botched copy of a vital gene from my mother be wholesale replaced by a
verbatim good copy from my father?

Yes. A *badly* botched copy from the mother. Not a simple base change.

And why?

Why not! If replication fails without this drastic step, give it a try!

Surely that much error
protection is too much (for evolution's sake)?

Depends on how frequent it is. My impression, from the molecular biology
texts, is that if you have a double-strand break - in effect, a broken
chromosome with some loss of genetic information by 'fraying' at the broken
edges - the best way of restoring something like the status quo is to
use the homologous chromosome as a model. And this actually takes place
in cells. And much of the machinery for this is the same as the machinery
for crossing-over during meiosis.

Now you point it out, I do recall reading about this several times!

Sometimes this machinery results in 'gene conversion' in which heterozygotes
become homozygotes for one or the other allele.

That would indeed be the consequence. My thought was that that is not
a particularly good outcome, considering the low cost of the
alternative, which is just to scrap the gamete when something like
this goes wrong. Perhaps I'm thinking too much about germ line
divisions. In somatic line divisions, such a repair policy may be
more justified (but even there, there is a lot to be said for zero
tolerance towards anything iffy).




.

Relevant Pages

  • Re: Evolution of Separate Genders in Animals
    ... separate genders, but did separate genders come before ... mean cell underwent meosis instead of mitosis, ... if that were the case we would need two organisms to ... for crossing-over during meiosis. ...
    (talk.origins)
  • Re: Evolution of Separate Genders in Animals
    ... mean cell underwent meosis instead of mitosis, ... if that were the case we would need two organisms to ... Meiosis is more complicated than you seem to think. ...
    (talk.origins)
  • Re: Evolution of Separate Genders in Animals
    ... separate genders, but did separate genders come before ... mean cell underwent meosis instead of mitosis, ... if that were the case we would need two organisms to ... systems intermediate between mitosis-only, and meiosis/fertilisation ...
    (talk.origins)
  • Re: Evolution of Separate Genders in Animals
    ... mean cell underwent meosis instead of mitosis, ... if that were the case we would need two organisms to ... Meiosis is more complicated than you seem to think. ...
    (talk.origins)
  • Re: Evolution of Separate Genders in Animals
    ... separate genders, but did separate genders come before ... mean cell underwent meosis instead of mitosis, ... if that were the case we would need two organisms to ... Exchange of transposons. ...
    (talk.origins)