Evolution: the Facts.

[Taffer]

Here's a question:

One of the human chromosomes is IIRC a doubling up of (a? two?) chimp ones.

I believe you are referring to the human chromosome 2, which has been formed by a fusing of two chimpanzee chromosomes. Or, rather, the fusing of two chimpanzee/human common ancestor chromosomes. AFAIK, all other major differences in chromsomal arrangement are inversions.

Now, would that (on its own) have altered the expression or function of any genes?

It might. Any scale of chromosomal rearrangement can have an effect on gene expression. To explain, there is a common trend to consider a gene as a descrete unit. I.e., just the sequence which is transcribed. However, it is becoming clear that this is a huge oversimplification. Genes are often associated into gene groups which show conserved synteny (linkage) between often very divergent taxa. (As an example of this, see this recent article in Science which compared complete genome sequences of the sea anemone Nematostella vectensis with other non-cnidarian^WP eumetazoans to attempt to approximate the ancient eumetazoan^WP common ancestor genome.) Given the hundreds of millions of years of evolution between the different taxa, either chromosomal rearrangements are very uncommon, or the synteny of these gene groups is being selectively maintained. On a smaller scale, just looking at the hox complex shows that gene arrangement plays a role in gene function.

So I guess my answer is: maybe. Certainly a gene's physical location on a chromosome can play a role in gene regulation and expression. However, it is also certainly not universally true. And given that the chromosomal rearrangement you are speaking of maintains the intrachromosomal synteny, it is unlikely that it would have had any effect. Of course, that being said, gene expression and regulation is far from simple. Sometimes even vary distant genes at opposite ends of a chromosome can show strong Linkage Disequilibrium^WP, and this is likely due to the physical characteristics of the chromosome.

I am guessing not, from the way that curent GM organisms are engineered.

As I said, is not even close to being universal. I would bet on there being no change whatsoever in gene expression.

Would that have been likely to to affect fertility between the two populations with the different chromosomes?


Regards

Jim

Yes it would, given that, because of the difference, chimpanzees and humans have different numbers of chromosomes. However, it might not be as simple as that. And an interesting question would be, did the hominin common ancestor have two chromosomes which were seperate, and have become fused in humans, or did the homonid^WP common ancestor have a fused chromosome, which was subsequently split in chimpanzees? A little digging shows that, AFAIK, all homonids except humans have two seperate chromosomes, so it is most parsimoniously explained as being a single split in the homo lineage.

(Links for clarification)

 

[arthwollipot]

The whole objective behind atheists bringing evolution into the discussion is with intent to prove there is no God.

Oh really? Since when?

Personally I started discussing evolution when I realised that creationists were telling outright lies about it. I felt a duty to point out to readers that what they were saying was factually incorrect. I wrote this about five years ago, and there's nothing in there about wanting to prove that there is no god (that was a different article - one which didn't mention evolution).

In my experience it has been Christians (or very occasionally Moslems or Raelians) who bring evolution into the discussion, not atheists. Well, most atheists anyway. Not all of us are atheist evangelists like Dawkins. I simply respond to specific claims made by the evolution-deniers.

Speaking from personal experience only, other atheists may have different stories.

 

[jimbob]

Taffer,
thanks for your responses in the post #208, your answers were roughly in line with what I guessed, including the "maybe's..."


This is the bit I think is interesting:

Quote:
Would that have been likely to to affect fertility between the two populations with the different chromosomes?

Yes it would, given that, because of the difference, chimpanzees and humans have different numbers of chromosomes. However, it might not be as simple as that. And an interesting question would be, did the hominin common ancestor have two chromosomes which were seperate, and have become fused in humans, or did the homonidWP common ancestor have a fused chromosome, which was subsequently split in chimpanzees? A little digging shows that, AFAIK, all homonids except humans have two seperate chromosomes, so it is most parsimoniously explained as being a single split in the homo lineage.

Now, do we have any idea as to when the split occured?

If such a split affected fertility, how did the original mutation spread, would siblings have been the answer? Or is the liklyhood just reduced, but still possible?

(I suppose an answer could be given if tigers and lions have different numbers of chromosomes, as (IIRC) a liger or tigon has managed to breed on at least one occasion).

A second answer is that either Chimps or humans have a different number of chromosomesfrom their common ancestor, and they have bread, so it is obviously possible...


Where is that neandertahl DNA? Is there any?

Jim

 

[sphenisc]

A little digging shows that, AFAIK, all homonids except humans have two seperate chromosomes, so it is most parsimoniously explained as being a single split in the homo lineage.

(Links for clarification)

Did you mean "fusion"?

 

[articulett]

Did you mean "fusion"?

Humans split from the ancestry... chromosome fused in the process.

 

[Taffer]

Did you mean "fusion"?

Er, yes.

 

[Taffer]

Taffer,
thanks for your responses in the post #208, your answers were roughly in line with what I guessed, including the "maybe's..."

This is the bit I think is interesting:

Now, do we have any idea as to when the split occured?

From what I remember of human evolution (and wiki seems to agree with me), the Hominini common ancestor lived around 5.4 to 6.3 million years ago. This was done, IIRC, through molecular clock estimations. See this paper for interest's sake.

If such a split affected fertility, how did the original mutation spread, would siblings have been the answer? Or is the liklyhood just reduced, but still possible?

(I suppose an answer could be given if tigers and lions have different numbers of chromosomes, as (IIRC) a liger or tigon has managed to breed on at least one occasion).

A second answer is that either Chimps or humans have a different number of chromosomesfrom their common ancestor, and they have bread, so it is obviously possible...

I'm not quite sure what you're asking here. If you are referring to what caused the speciation event which lead to humans and chimpanzees? Or are you asking what effect the fusion of the chromosomes had on speciation?

Where is that neandertahl DNA? Is there any?

Jim

Oh yes, definately. Here, here and here for example.

 

[jimbob]

Thanks,

I was sort of asking two questions:


1) Did the chromosomal difference lead to, or help, speciation

2) When the number of chromosomes changed how did those "mutants" breed? Wouldn't they have been more likely to breed with organisms with the same number of chromosomes as themselves, i.e. no other organism?

 

[Taffer]

Thanks,

More then welcome, actually. It's nice to be able to use all that useless knowledge they stuff into our heads.

I was sort of asking two questions:

1) Did the chromosomal difference lead to, or help, speciation

It probably played some part. But it is hard to tell if the speciation led to the split, or the split led to the speciation. If I had to make a guess, I would guess that the split arose after the speciation event. Just a gut feeling.

2) When the number of chromosomes changed how did those "mutants" breed? Wouldn't they have been more likely to breed with organisms with the same number of chromosomes as themselves, i.e. no other organism?

This is always an interesting question. I'm not really qualified to answer it, to be honest. The best I can do is point at plants. They can do all sorts of really weird things with different numbers of chromosomes. But it is a good question, none-the-less. It's interesting to think that, in general, large-scale chromosomal rearrangements are rare. However, that being said, the split could have arisen through an intermediate state which we are not seeing. For example, if the un-split chromosome was duplicated with no ill effect, this could spread throughout a population. Then, when the chromosome splits, breeding with an individual without the split doesn't lead to a child with any lost chromosomal 'information'.

Speculation, to be sure, and possibly the best we will ever get.

 

[The Atheist]

P.S: this is kind of tangential but I just wrote [swiki]Laws of Nature[/swiki], to go in the Principles of Science section. Again, please let me know what you all think.

Brilliant! Highly understandable, succinct and entirely relevant.

 

[articulett]

That Dawkins youtube simulation of clock parts ending up as functional clocks was the best visual interpretation of the process I've ever seen. Now, where's the bloody link gone?

http://www.youtube.com/watch?v=mcAq9bmCeR0

or this http://www.youtube.com/watch?v=Ex4O5z_ig2g

 

[Miss Anthrope]

Per repeated requests, posts that were off topic and derailed the discussion have been split into religion and philosophy. Posts on this thread should address the OP and follow the flow of discussion.

Replying to this modbox in thread will be off topic  Posted By: Miss Anthrope

 

[Dr Adequate]

[swiki]Biogeography[/swiki]. One of those subjects, like behavioral ecology, that doesn't get talked about nearly enough.

And [swiki]Means of Dispersal[/swiki] as a supporting article.

Also, there's a chap called The Matt on EvC forums who's doing a thread on geology for beginners, who says the SW can use his text once he's polished it up a bit.

Meanwhile, I notice a lot of tumbleweed blowing around here.

Hey, that's a means of dispersal!

P.S: Does anyone have any idea how I should illustrate the article on biogeography? Dodos are so cliched --- mind you, so are dandelion seeds for means of dispersal.

 

[The Atheist]

P.S: Does anyone have any idea how I should illustrate the article on biogeography?

There's a good favourite of biologists right here - New Zealand. Unique species, early separation of land mass, no native mammals, lots of extinct species.

 

[Dr Adequate]

I meant "illustrate" as in pretty pictures.

NZ nearly made it to the "examples" section for having ratites but no non-flying mammals. Incidentally, is it you guys who have the bat that hunts on the forest floor at night?

 

[John Smith]

Creationists believe what they want to believe, whereas scientists begrudgungly accept what the data points towrads, which doesn't always feel so good.

 

[The Atheist]

I meant "illustrate" as in pretty pictures.

Lots of pretty birds amaong them and the moa is always impressive.

NZ nearly made it to the "examples" section for having ratites but no non-flying mammals. Incidentally, is it you guys who have the bat that hunts on the forest floor at night?

Yep, this one.

They aren't very common, unfortunately. Not only have I never seen one, I don't even know anyone who has.

 

[Dr Adequate]

[swiki]Evolutionarily Stable Strategies[/swiki]

Not only interesting in itself, but a clear example of how under certain circumstances evolution must produce results different to those that would be produced by truly intelligent design.

 

[The Atheist]

Brilliantly done again.

It seems that you'll have the whole thing done in SW given enough time. That's probably to the good, although I have a couple of questions about SW which I'll put up in Community.

 

[Dr Adequate]

Your writing is kind of intimidating...
I feel like my entries would be so much less "scholarly" in comparison.

So really it's my fault.

* kicks furniture *