Are humans apes?

[Horwood Beer-Master]

...This is right, a species of mouse from Japan comes to mind, I may dig up some research papers later on this.

I'm glad someone remembers the details, for some reason I was (vaguely) thinking it was a species of antelope or something (Or maybe I remembered correctly, and there is a species of antelope that has this trait as well - more likely it was the mouse I'd heard of and my memory's just being useless as usual)

[GenesForLife]

Abstract Chromosome studies were made on 74 animals of the field mouse, Apodemus giliacus, a new form of the genus Apodemus described by Kobayashi and Hayata (1970). Extreme variations in number and morphology of chromosomes was observed. While the diploid numbers varied from 48 to 61, the number of acrocentric elements was consistently 48, except for one specimen which had 40 such elements. In contrast, the number and constitution of several biarmed elements and microchromosomes were highly variable in the complement, and, hence, responsible for the polymorphism. Karyotype analysis of meiotic chromosomes, on the basis of Giemsaand quinacrine-stained preparations, some familial studies and breeding experiments revealed that variable elements were supernumeraries of a hitherto undescribed type, whereas the 48 acrocentrics seemed to represent regular autosomes and sex elements. Most of the supernumeraries did not show pairing at metaphase I, but some did form bivalents. Usually, the supernumerary biarmed chromosomes were of regular size and fluoresced rather brightly over their entire length, suggesting that they were heterochromatic in nature. Considering the above findings and other relevant data of some allied species, the differentiation between A. giliacus and A. speciosus might have occurred rather recently, when the former species might have been involved in rapid and divergent chromosomal evolution.

http://www.springerlink.com/content/q138q27267360j61/

[Ironclad]

The family Hominidae is referred to as the 'Great Apes' and contains Gorillas, Orang Utans, Chimpanzees and Humans. The lesser apes contain such creatures as baboons and pawiz.

[Xamonas Chegwé]

The family Hominidae is referred to as the 'Great Apes' and contains Gorillas, Orang Utans, Chimpanzees and Humans. The lesser apes contain such creatures as baboons and pawiz.

Sorry, and Ironclad.

[mistermack]

As far as the fusion of the chromosomes causing a barrier to reproduction, I still think that it's unlikely that it did six million years ago, at the time of the speciation event.
The genes that caused the fusion must have successfully flourished in the population, to become common enough to get fixed.
Simple logic says that if a gene contributed to a barrier to reproduction, it's unlikely to flourish. If the fused chromosomes are a barrier, it's more likely that that happened later, after some considerable time of seperate evolution.

[JimC]

As far as the fusion of the chromosomes causing a barrier to reproduction, I still think that it's unlikely that it did six million years ago, at the time of the speciation event.
The genes that caused the fusion must have successfully flourished in the population, to become common enough to get fixed.
Simple logic says that if a gene contributed to a barrier to reproduction, it's unlikely to flourish. If the fused chromosomes are a barrier, it's more likely that that happened later, after some considerable time of seperate evolution.

Genes do't cause a chromosome fusion - the actual genes involved are identically present on the fused and non-fused chromosomes. I believe it can best be described as accidental, either in meiosis, of in fertilisation.

The gradual accumulation of genetic changes in separated populations is indeed the classic way that sufficient reproductive isolation develops to stop the populations merging when and if they later meet; this is the standard basis for allopatric speciation. The fusion event, however, could have provided an immediate population barrier, meaning that geograhic separation was not so vital. I agree the jury is still out as to whether it actually happened that way, but it is certainly possible.

[mistermack]

Genes do't cause a chromosome fusion - the actual genes involved are identically present on the fused and non-fused chromosomes. I believe it can best be described as accidental, either in meiosis, of in fertilisation.

I can't agree with that, but I think we're at cross purposes here.
Genes DO cause a chromosome fusion.
But I'm not talking about the genes held INSIDE the fusing chromosomes.
I'm talking about the genes that PRODUCE the chromosomes that are prone to fuse.
The makeup of the chromosomes is anything but accidental. It's a direct result of the genes that made them.
It's these genes that would be very unlikely to flourish, or even survive, if they produced chromosomes that fuse and inhibit reproduction.

Or to put it more simply, how can a feature that blocks fertility successfully evolve and spread in a population?

[Xamonas Chegwé]

Genes do't cause a chromosome fusion - the actual genes involved are identically present on the fused and non-fused chromosomes. I believe it can best be described as accidental, either in meiosis, of in fertilisation.

I can't agree with that, but I think we're at cross purposes here.
Genes DO cause a chromosme fusion.
But I'm not talking about the genes held INSIDE the fusing chromosomes.
I'm talking about the genes that PRODUCE the chormosomes that are prone to fuse.
The makeup of the chromosomes is anything but accidental. It's a direct result of the genes that made them.
It's these genes that would be very unlikely to flourish, or even survive, if they produced chromosomes that fuse and inhibit reproduction.

Or to put it more simply, how can a feature that blocks fertility successfully evolve and spread in a population?

If it was initially only a partial block to fertility.

If the chances of producing a viable offspring when both parents had the fused chromosome were significantly greater than the chances when only one did, and the trait were dominant, eventually a sub-population would emerge. Subsequent changes in that population could then cause further genetic isolation.

This seems a possible mechanism for me - unless the mutation occured in several members of the same population at the same time, which is seriously unlikely.

[JimC]

From Wikipedia: this link

The results of the chimpanzee genome project suggest that when ancestral chromosomes 2A and 2B fused to produce human chromosome 2, no genes were lost from the fused ends of 2A and 2B. At the site of fusion, there are approximately 150,000 base pairs of sequence not found in chimpanzee chromosomes 2A and 2B. Additional linked copies of the PGML/FOXD/CBWD genes exist elsewhere in the human genome, particularly near the p end of chromosome 9. This suggests that a copy of these genes may have been added to the end of the ancestral 2A or 2B prior to the fusion event. It remains to be determined if these inserted genes confer a selective advantage.

Genes do't cause a chromosome fusion - the actual genes involved are identically present on the fused and non-fused chromosomes. I believe it can best be described as accidental, either in meiosis, of in fertilisation.

I can't agree with that, but I think we're at cross purposes here.
Genes DO cause a chromosome fusion.
But I'm not talking about the genes held INSIDE the fusing chromosomes.
I'm talking about the genes that PRODUCE the chromosomes that are prone to fuse.
The makeup of the chromosomes is anything but accidental. It's a direct result of the genes that made them.
It's these genes that would be very unlikely to flourish, or even survive, if they produced chromosomes that fuse and inhibit reproduction.

Or to put it more simply, how can a feature that blocks fertility successfully evolve and spread in a population?

For a start, I think it is misleading to say that genes cause a chromosome fusion. I'm not sure whether it has been established how common chromosome fusion is, and whether it is more prevalent in certain chromosomes in certain species, or simply a rare and accidental fault in the mechanism of meiosis. As for the blocking of fertility, that is only between the sub-population which descended from an individual, or small group (possibly siblings) with the fusion, and the ancestral population without. There does not need to be any reduction of fertility within that sub-population.

[mistermack]

Or to put it more simply, how can a feature that blocks fertility successfully evolve and spread in a population?

If it was initially only a partial block to fertility.

If the chances of producing a viable offspring when both parents had the fused chromosome were significantly greater than the chances when only one did, and the trait were dominant, eventually a sub-population would emerge. Subsequent changes in that population could then cause further genetic isolation.

This seems a possible mechanism for me - unless the mutation occured in several members of the same population at the same time, which is seriously unlikely.

Possible I suppose, but a bit contrived. To get to the point where both parents had fused chromosomes, you have already reached the point where the change had evolved and flourished to become common. So you still don't have a mechanism for it to go from being a rare or unique occurrence, to being a common feature.

[JimC]

[Or to put it more simply, how can a feature that blocks fertility successfully evolve and spread in a population?

If it was initially only a partial block to fertility.

If the chances of producing a viable offspring when both parents had the fused chromosome were significantly greater than the chances when only one did, and the trait were dominant, eventually a sub-population would emerge. Subsequent changes in that population could then cause further genetic isolation.

This seems a possible mechanism for me - unless the mutation occured in several members of the same population at the same time, which is seriously unlikely.[/quote}
Possible I suppose, but a bit contrived. To get to the point where both parents had fused chromosomes, you have already reached the point where the change had evolved and flourished to become common. So you still don't have a mechanism for it to go from being a rare or unique occurrence, to being a common feature.
.

I agree it has some puzzling features; perhaps it occurred in one mating pair in a founder population, separated from the main population, and the siblings all had the fusion feature, bred successfully amongst themselves, and it was off. Such a small starting population should leave clear signs, though, like Cheetahs.

However, the fact that all the great apes except us have one more pair of chromosomes suggest that it was an significant part of the divergence from the ancestral chimp-like ancestor. I would also be prepared to bet that it would make successful reproduction between fused and unfused indiviuals very unlikely. Ethical issues aside, I wonder if anybody has tried to combine human and chimp eggs and sperm, and see what happens (only to blastocyst stage, if it even reached that...)

I am certainly willing to say that all my posts in this area are speculative indeed...

[mistermack]

It is interesting. I'm only saying genes cause fusion, in the same sense that genes cause absolutely everything.
There's no doubt it happened. It could be down to a radiation from a tiny population, but you would think the markers of that would be unmistakeable.
If as I was suggesting, the fusion wasn't an effective block initially, it had to BECOME at least a partial block later, because the unfused Chromosomes have died out. It wouldn't have to be a 100 percent block for that to happen. Just enough to numerically favour the fused individuals, at the expense of the unfused. You would eventually get extinction of the unfused trait.
So it could have had a role in reinforcing the split, and making sure it wasn't reversed later.
I don't think that anyone has ever had the nerve to try cross fertilisation, or at least, not to admit to it.

[JimC]

It is interesting. I'm only saying genes cause fusion, in the same sense that genes cause absolutely everything.
There's no doubt it happened. It could be down to a radiation from a tiny population, but you would think the markers of that would be unmistakeable.
If as I was suggesting, the fusion wasn't an effective block initially, it had to BECOME at least a partial block later, because the unfused Chromosomes have died out. It wouldn't have to be a 100 percent block for that to happen. Just enough to numerically favour the fused individuals, at the expense of the unfused. You would eventually get extinction of the unfused trait.
So it could have had a role in reinforcing the split, and making sure it wasn't reversed later.
I don't think that anyone has ever had the nerve to try cross fertilisation, or at least, not to admit to it.

In Melbourne University in the 70s, I (as an honours student) was part of a group studying groups of closely related species of treefrogs (hence the avatar... ). Before more elaborate tests came along, one of the methods we used to get some idea of how close various species were to each other genetically was in vitro hybridisation. Essentially, you would get a gravid female of 1 species, strip her of eggs, then dissect out the testes of a male of another species, crush them, mix them with pond water, and add them to the eggs. In amphibians, fertilisation is of course external, so this mimicked nature quite well... (of course, you would always do a control of a within species cross, which should produce perfect tadpoles...)

Results varied from no fertilisation at all (typically between species from different genera), through to various proportions of deformed tads, and then to normal looking tads that wouldn't metamorphose, etc...

Essentially, the % of deformities or problems was reckoned to be a rough guide to the degree of genetic divergence. Typically, it usually mirrored quite well evidence from morphological differences etc...

[GenesForLife]

Genes do't cause a chromosome fusion - the actual genes involved are identically present on the fused and non-fused chromosomes. I believe it can best be described as accidental, either in meiosis, of in fertilisation.

I can't agree with that, but I think we're at cross purposes here.

Let's see where we go with this.

Genes DO cause a chromosome fusion.

You have evidence for these kinds of genes?

But I'm not talking about the genes held INSIDE the fusing chromosomes.
I'm talking about the genes that PRODUCE the chromosomes that are prone to fuse.

Again, a citation is required for this.

The makeup of the chromosomes is anything but accidental. It's a direct result of the genes that made them.
It's these genes that would be very unlikely to flourish, or even survive, if they produced chromosomes that fuse and inhibit reproduction

.

Well, new chromosomes are formed by replication, so this is rather bleeding obvious, firstly.
Secondly, I do not think fusion is deleterious as long as there is no large scale genetic loss of vital genes in the process.

Or to put it more simply, how can a feature that blocks fertility successfully evolve and spread in a population?

I need another citation to demonstrate that chromosome fusion blocks fertility.

[mistermack]

You have evidence for these kinds of genes?

Genes produce every characteristic. So they produce the tendency for chromosomes to fuse. Take two populations. One with fused chromosomes. One with seperate. What's the difference? A GENETIC difference.

Well, new chromosomes are formed by replication, so this is rather bleeding obvious, firstly.

Really? We are talking about SEXUAL reproduction here. You have chromosomal crossover, so it's hardly simple replication.

Secondly, I do not think fusion is deleterious as long as there is no large scale genetic loss of vital genes in the process.

Well, that clears the matter up. If YOU can provide a citation?

I need another citation to demonstrate that chromosome fusion blocks fertility.

You seem to have missed the point by a mile, and driven on another ten miles.
That's the point under debate here. If we had citations, we wouldn't need to debate it.