clipka wrote:
> In case of a basic change of the genetic structure, like a different number of
> chromosomes, this appears quite amazing, because obviously it cannot evolve
> over time so (a) cannot play a role, and (b) seems unlikely due to the dramatic
> proportions of the change.

http://en.wikipedia.org/wiki/Down_syndrome

> So intially the 47-chromosome population must have been comparatively
> successful.

Or it's less hard to combine 48 with 46 than you might think. All the data 
is there, including the tollermerines (or however you spell it) in the middle.

-- 
   Darren New, San Diego CA, USA (PST)
   "We'd like you to back-port all the changes in 2.0
    back to version 1.0."
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On 19-7-2009 19:34, Darren New wrote:
> clipka wrote:

>> So intially the 47-chromosome population must have been comparatively
>> successful.
> 
> Or it's less hard to combine 48 with 46 than you might think. All the 
> data is there, including the tollermerines (or however you spell it) in 
> the middle.
centromere?
I don't think everything is preserved, there may be a small part 
missing, I assume that is more than just the telomeres (if that is the 
other word you were looking for ;) ):
http://www.don-lindsay-archive.org/creation/translocation.html
apparently that was not crucial.
One reason to bring this point up is that the difference in chromosome 
number is mentioned as one of the reasons why we can not interbreed with 
chimps. If that is the case than you can not have different numbers of 
chromosomes in various species. But you do, hence it must be more subtle 
than that. When it first happens crossover during meiosis may be 
impaired in the 47 chromosome individuals, but as long as the rest 
matches, we can apparently get away with it.

Some random thoughs (that I am not sure if I tried those out here before)
The individual in which this translocation happened is undoubtedly one 
of the ancestors of all men (as are the individuals in which the 
inversions first appeared).* Slightly more speculative is my guess that 
this or one of the inversions was the mutation that caused a form of 
neotony in that ancestor. That would have resulted in a less strong but 
more 'intelligent' individual. Which would have been a handicap in the 
chimp and to a lesser extend the bonobo type of society for a male but a 
huge advantage for a female. Hence: I think that particular ancestor was 
a female (one of our Eves). It would be interesting to try to date those 
mutations.

* if we have 30000 genes and we have 98% of our genes in common with the 
two species of chimp than there are at least 300 ancestors common to all 
humans since our split of the chimp line, and probably much more.

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On 19-7-2009 19:09, clipka wrote:
> andrel <a_l### [at] hotmailcom> wrote:
>> You are not able to interbreed with chimps and bonobos. Not only because
>> you find them (probably) unattractive but also because our genes do not
>> match. Somewhere along the line two chromosomes fused to one bigger one,
>> so that we now have 23 pairs of them and the chimp still 24. There are
>> also some other large reshuffelings of genes that will prevent mixed
>> offspring. How the 46/48 chromosome hybrids ever were compatible is a
>> thing that amazes me everytime, but that is something for another
>> discussion.
> 
> But I guess this is exactly the point creationists will make.
> 
> In order for evolution to work with sexual reproduction to produce new species,
> there *must* always be a phase where the two subspecies still *can* interpreed
> (genetically), but are less *likely* to do so successfully, because either...
> 
> (a) they're genetically fully "compatible" with one another but separated into
> different populations, or
> 
> (b) they're *slightly* less "compatible" with one another (e.g. having a higher
> rate of birth defects, or invariably having offspring that have a minor genetic
> disadvantage).
> 
> In case of a basic change of the genetic structure, like a different number of
> chromosomes, this appears quite amazing, because obviously it cannot evolve
> over time so (a) cannot play a role, and (b) seems unlikely due to the dramatic
> proportions of the change.
As Darren pointed out, a different number of chromosomes may have severe 
consequences when that is because one chromosome did not make it to the 
next generation or if there is a duplication. (if there is down there 
must also have been fertilized eggs with one chromosome 21 missing. I 
think we can safely assume that is not compatible with life). Luckily in 
our case it was a fusion of two chromosomes into one.
http://www.don-lindsay-archive.org/creation/translocation.html

> 
> BTW, the compatibility of the 46- and 48-chromosome population is very unlikely
> to have been a problem: They would invariably have carried 23+24 chromosome
> (i.e. 47 chromosome). They *must* have been compatible to some degree, because
> the first mutation will in all likelyhood have affected only *one* chromosome
> set, producing such a 47-chromosome individual.
> 
> This 47-chromosome individual must have proven successful enough to spread this
> trait (with only 48-chromosome individuals available as partners, half of its
> offspring would have had the regular set of 48 chromosomes, the other half 47
> chromosomes, though there's reason to expect a higher percentage of
> miscarriages or other complications in the 47-chromosome offspring), and its
> offspring likewise, so that the 47-chromosome population could become large
> enough to mate among themselves.
As incest is not common among chimps, we need at least two successful 
generations of 47 chromosomes.


> Only thus was it possible to produce the first 46-chromosome offspring (47/47
> parents would have 25% 48-chromosome, 50% 47-chromosome and 25% 46-chromosome
> offspring; again, the percentage of offspring actually born is likely to have
> been different).
yes, they were probably different.
> 
> So intially the 47-chromosome population must have been comparatively
> successful.
not necessarily. I also like to speculate on what happened, the problem 
is a bit that we are reasoning from the fact that we know that in the 
end humanity arose. Take also into account that the bottleneck between 
chimps and humans is estimated at at least 1000 individuals, then it is 
clear that interbreeding must have been possible for some time (and that 
that bottle neck may not have been at this point in time).

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andrel wrote:
> As Darren pointed out, a different number of chromosomes may have severe 
> consequences when that is because one chromosome did not make it to the 
> next generation or if there is a duplication.

I don't know what point you thought I was trying to make.  My point is that 
organisms are extremely robust to screwed up genetics. You can give someone 
and extra chromosome and they can still function.

I wouldn't want to gamble that someone with a different number of 
chromosomes couldn't possibly have viable offspring. Not common, mind, but 
impossible?  I don't know enough to say.

> chimps and humans is estimated at at least 1000 individuals, then it is 

I read recently that cheetahs don't reject organ transplants from other 
cheetahs, and that looking at the chromosomes, one can tell that at one 
point there were only 6 or 7 cheetahs in the world.

-- 
   Darren New, San Diego CA, USA (PST)
   "We'd like you to back-port all the changes in 2.0
    back to version 1.0."
   "We've done that already. We call it 2.0."

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andrel <a_l### [at] hotmailcom> wrote:
> * if we have 30000 genes and we have 98% of our genes in common with the
> two species of chimp than there are at least 300 ancestors common to all
> humans since our split of the chimp line, and probably much more.

According to http://www.genetics.org/cgi/content/full/156/1/297, it's 199
differences.

Furthermore, there are two basic fallacies in this argumentation:

* Given that the average number of mutations *per individual* is estimated at
about ~175 (!) in each generation (see aforementioned article - man, I confess
this sounds crazy!), all these 199 differences might have been acquired in just
one or two generations.

* It is not even necessary for all of these mutations to have occurred *after*
the split of the chimp/human line. Some may have been genetic differences that
were introduced earlier in the common ancestors of chimps and humans, but with
each variant prevailing in only one branch.

For instance, such a gene may have affected some aspect of visual appearance
which our common ancestors did not care much about, but which may have had a
beneficial side-effect for the new 46-chromosome group, therefore becoming more
and more frequent among it as the groups evolved apart; another mutation may
then have spread in the 48-chromosome group to consider this visual feature
unpleasant, further reducing the interbreeding rate and at the same time
beginning to extinguishing that feature in the 48-chromosome group.


So all we can really say about it all is that there is at least *one* common
ancestor to all humankind with any relation to the chimp/human separation: The
individual to be the first with 47 instead of 48 chromosomes.

Of course, given how many generations have passed since then, there is reason to
argue that virtually all early "46-chromosomians" that are ancestors to *any*
modern human can be expected to actually be ancestors of *all* modern humans -
even if some may not have left any trace in the modern human's gene pool, and
only very few (at *most* 199 :)) have passed on particular genes to *all*
modern humans.

Given this relationship, there's also reason to argue that the 199 genetic
differences between humans and chimps accumulated over time after all, and that
therefore indeed roughly 199 of our many common ancestors may have passed a part
of their genome on to *all* modern humans after all.

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clipka wrote:
> For instance, such a gene may have affected some aspect of visual appearance
> which our common ancestors did not care much about, but which may have had a
> beneficial side-effect for the new 46-chromosome group, therefore becoming more
> and more frequent among it as the groups evolved apart; another mutation may
> then have spread in the 48-chromosome group to consider this visual feature
> unpleasant, further reducing the interbreeding rate and at the same time
> beginning to extinguishing that feature in the 48-chromosome group.
> 

This reminds me of the video I saw recently, and computer generated 
extrapolation of the changes in morphology between the earliest human 
ancestor skull, and a modern human, showing how each "tiny" change can, 
over time, result in such a drastic one.

Mind, the music is kind of stupid, and the words they flash up once in a 
while are kind of lame, but, otherwise:

http://www.youtube.com/watch?v=EcqA8wEljPM

Ah, they have a "class room" version without the lame stuff in it too:

http://www.youtube.com/watch?v=GrhYLvNeQd4

-- 
void main () {

     if version = "Vista" {
       call slow_by_half();
       call DRM_everything();
     }
     call functional_code();
   }
   else
     call crash_windows();
}

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3D Content, and 3D Software at DAZ3D!</A>

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John VanSickle wrote:
> Darren New wrote:
>> Well, so much for the old "we've never seen it happen, so it can't."
>>
>>
http://www.geneticarchaeology.com/research/Study_catches_2_bird_populations_as_they_split_into_separate_species.asp

> 
> 
> We haven't seen it happen yet. 

Actually we have, dozens of times. This is just an example of "on the cusp." 
But that's OK. :-)

-- 
   Darren New, San Diego CA, USA (PST)
   "We'd like you to back-port all the changes in 2.0
    back to version 1.0."
   "We've done that already. We call it 2.0."

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Darren New <dne### [at] sanrrcom> wrote:
> Or it's less hard to combine 48 with 46 than you might think. All the data
> is there, including the tollermerines (or however you spell it) in the middle.

Just happened to stumble across the Wikipedia articles on mules and hinnys
(citing the latter here):

"A donkey has 62 chromosomes, whereas a horse has 64. Hinnies, being hybrids of
those two species, have 63 chromosomes and are sterile."

But later on the article reveals that this is an oversimplification:

"Female mules have been known to produce offspring when mated to a purebred
horse or donkey, though this is extremely uncommon."


Duh. Didn't know that horses and donkeys have different numbers of chromosomes,
too (then again, it was news to me as well that chimps and humans have).

So this makes me think that...

- mutations changing the number of chromosomes don't seem to be as uncommon as I
had thought

- with mules and hinnys being perfectly viable and typically not showing any
other defects, and even *not always* being sterile, this gives rise to the
assumption that having an odd number of chromosomes is an absolutely
non-dramatic mutation as such (why should *only* the reproductive system show
issues? and why not always?), and that the sterility is instead imposed by
other genetic mechanisms "designed" (by evolution) to separate the two gene
pools.

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clipka wrote:
> "Female mules have been known to produce offspring when mated to a purebred
> horse or donkey, though this is extremely uncommon."

Yes. This is another one of those "on the cusp of becoming two species."  It 
really isn't as uncommon as people think.

-- 
   Darren New, San Diego CA, USA (PST)
   "We'd like you to back-port all the changes in 2.0
    back to version 1.0."
   "We've done that already. We call it 2.0."

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On 21-7-2009 18:15, clipka wrote:
> Darren New <dne### [at] sanrrcom> wrote:
>> Or it's less hard to combine 48 with 46 than you might think. All the data
>> is there, including the tollermerines (or however you spell it) in the middle.
> 
> Just happened to stumble across the Wikipedia articles on mules and hinnys
> (citing the latter here):
> 
> "A donkey has 62 chromosomes, whereas a horse has 64. Hinnies, being hybrids of
> those two species, have 63 chromosomes and are sterile."
> 
> But later on the article reveals that this is an oversimplification:
> 
> "Female mules have been known to produce offspring when mated to a purebred
> horse or donkey, though this is extremely uncommon."
> 
> 
> Duh. Didn't know that horses and donkeys have different numbers of chromosomes,
> too (then again, it was news to me as well that chimps and humans have).
> 
> So this makes me think that...
> 
> - mutations changing the number of chromosomes don't seem to be as uncommon as I
> had thought

http://en.wikipedia.org/wiki/List_of_number_of_chromosomes_of_various_organisms
is hard to explain otherwise.

> - with mules and hinnys being perfectly viable and typically not showing any
> other defects, and even *not always* being sterile, this gives rise to the
> assumption that having an odd number of chromosomes is an absolutely
> non-dramatic mutation as such (why should *only* the reproductive system show
> issues? and why not always?), and that the sterility is instead imposed by
> other genetic mechanisms "designed" (by evolution) to separate the two gene
> pools.

I guess how dramatic it is, is variable. For those that we know of it is 
not an extreme problem. Where 'know of' is the important bit. If the 
translocation that resulted in our chromosome 2 would not have been 
viable or have been sterile, we would not have known.
You know of trisomy 21 because it is common, viable, and recognizable. 
According to wikipedia trisomy 16 is actual the most common, guess why 
you have never heard of it.

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