Talk:Chromosome 2

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Some text in this article was taken from http://ghr.nlm.nih.gov/chromosome=2 (public domain)

Post-Fusion evolution

If you are familiar with the chromosome fusion event, please explain how it was possible for the first individual with a fused chromosome 2 to find a mate with a similarly fused chromosome 2.

The following explanations come to mind:

1. Perhaps one individual ape had a random, dominant mutation that caused all or most of his/her descendants to have chromosome 2 fusions. Inbreeding between those descendants resulted in a new species (humans) that could not breed with non-humans.

2. Perhaps a random, dominant mutation temporarily suppressed the genetic mechanism that causes fetal death when mismatched chromosomes are detected, so that individuals with fused chromosome 2 (i.e. humans) were able to successfully breed with non-humans who did not have fused chromosome 2, and some of the resulting descendants retained that mutation for a few generations. But eventually the mutation was lost and thereafter no humans retained the mutation that made human/ape mating possible.

3. Perhaps there was a dominant pre-fusion mutation in one ape that was copied into all descendants, all of which had unfused 2a and 2b chromosomes and this permitted sucessful mating with non-mutated apes. Perhaps fusion resulted if both male and female carried the pre-fusion mutation but no fusion if only one carried it. And perhaps those with fusion could successfully mate with non-fused apes that had the pre-fusion mutation and produce babies with fusion.

Reliable references for such explanation(s) are needed. Greensburger (talk) 06:09, 9 May 2010 (UTC)

I can't claim to be "familiar with the . . . event" even on a theoretical basis, but from my lay standpoint I can't see any particular problem. In the first individual(s) with the fusion, the two separate chromosomes from an unmutated mate would presumably still have been able to align with the end-fused version without (much) difficulty, and there would have been little or no discernable effect. As the fused version proliferated in the population, some fused-fused pairings would also have occurred with increasing frequency. Over (long) time, reductions of the fused telomeres and doubtless other changes would have made successful fused-unfused pairings increasingly less likely to be successful, and gradually two "cryptic-species" (see Cryptic species complex) would have developed, though for a very long time they would not have appeared phenotypically different. Speciation is, I think, rarely a single generational event; more often it will take hundresds to thousands of generations. 87.81.230.195 (talk) 17:01, 13 May 2010 (UTC)

Perhaps only a dozen or so generations were sufficient to produce thousands of apes with the pre-fusion mutation. If inbreeding between apes with the pre-fusion mutation resulted in fusion, speciation could result in only one generation, consisting of hundreds of babies that had the fusion. If the fusion conferred only one significant survival advantage (for example patches of bare skin that produced more vitamin D), most of the next generation could be fused because they were healthier and produced more healthy babies. Greensburger (talk) 02:51, 14 May 2010 (UTC)

Perhaps, but also perhaps not, depending on how large (and dense) the population was (aside from any actual genetic viability problems). I believe current thinking is that the absolute numbers of our ancestral species (plural) were quite low and also that they (due to their ecological niches) may have been quite thinly dispersed, so proliferation of the fused genes might also have been slow. We also don't (so far as I know) have a good idea of how long it would have taken for fused-unfused interfertility to develop, nor do we know if either of your "ifs" were actually the case. At this stage of our knowledge much about our speciation is still speculation. I too would welcome guidance to further references on these questions, if any exist. 87.81.230.195 (talk) 16:46, 14 May 2010 (UTC)

Evolution

However, an important point is that a significant difference between humans and apes is the number of chromosomes; yet that difference turns out to be simply the result of a fusion. In other words, even if your argument is correct, the fusion still provides some support for common descent (at least, the fusion makes common descent less unlikely). The critical factor is what reliable sources say, and your change to the article is not sourced (and therefore may breach WP:NOR). Johnuniq (talk) 03:33, 12 October 2010 (UTC)

The problem with that argument is this: there are two scenarios we can consider--evolution by natural selection and creation. If evolution by natural selection is true, then we would definitely need some kind of major event that explains why humans have 23 pairs and the other apes have 24. This fusion provides that evidence. In that sense, yes, the fusion event is consistent with what we would expect from evolution. However, now consider creationism. A creationist would argue that a deity created all the hominids at some time in the past. They would all share genetic similarity because they are all phenotypically similar--similar things share similar DNA. If humans have 23 pairs now, with evidence that we had 24 pairs in the past (the remnant centromere and telomeres), then that could be interpreted such that humans were created with 24 pairs and sometime after the creation event we experienced a fusion event that led to 23 pairs. In other words the fusion event carries no explanatory power and does not lend evidence either one way or the other. If we're going to specifically point out that the fusion event is evidence for common descent, then we also have to point out that the fusion event is evidence that a fusion event occurred after the creation event. Also, I provided a novel thought experiment. Do novel thought experiments need sources? Chungdoh (talk) 14:29, 12 October 2010 (UTC)

The point here is that - using scientific knowledge about evolution and genetics - it was predicted that this fusion site would exist at some location in the human genome. And, lo and behold, it has indeed been found. I don't really get what is so hard to understand about this? The predictive power of established scientific principles is what makes them useful and shows that they represent truth, in a way that anything unevidenced doesn't. If you are suggesting there is no dichotomy between evolution and creation, as you seem to be doing in the last few sentences, I don't know what you are talking about: creationists believe humans were created as we are now. 89.98.179.2 (talk) 00:06, 20 February 2014 (UTC)

I suggest you move your arguments to this discussion page in hopes that a knowledgeable biologist will provide a reference in the article. You state without evidence that "the fusion of two ancestral chromosomes into human chromosome 2 presumably occurred after the human line split from the remainder of the great apes". It is also possible that the split of the ape line from the human line occurred long after the fusion event and the early fusion apes may have had no human traits except one that gave them greater survival value than the non-fusion apes which compensated for their small numbers. Much later, there may have been a series of mutations that gave a sub species of the fused apes several more human characteristics while the non-human fused apes became extinct. Greensburger (talk) 03:46, 12 October 2010 (UTC)

"It is also possible that the split of the ape line from the human line occurred long after the fusion event..." If that were the case, then all extant apes would also carry the fusion, which they don't. Chungdoh (talk) 14:17, 12 October 2010 (UTC)

We don't know how stable the fusion event was. Perhaps thousands of apes had a pre-fusion mutation (all descended from one common ancestor) which resulted in a stable fusion if their mates also had the pre-fusion mutation and many of their descendants had the fusion and this was the human line. But perhaps the fusion event was not a clean break and may have been fragile in descendants of matings of fusion apes with non-fusion apes and all of these either became extinct or perhaps led to the the chimp line. If anyone has tried fusing chimp 2a and 2b to determine what is or is not viable, please describe the results in this article. Greensburger (talk) 04:48, 10 November 2010 (UTC)

The Humanzee article includes this reference: "In 2006, research suggested that after the last common ancestor of humans and chimpanzees diverged into two distinct lineages that produced fertile hybrids for around 1.2 million years after the initial split." Greensburger (talk) 18:46, 10 November 2010 (UTC)

Further information on fertile hybrids can be found at Chromosomal polymorphism. Greensburger (talk) 15:06, 29 December 2010 (UTC)

Chungdoh's insertion is now being cited by Creationists on other sites as proof that "Even Wikipedia agrees this isn't evidence for common descent." As he hasn't provided sources, I move to revert. Any objections? --BRPierce (talk) 20:22, 11 November 2010 (UTC)

No objection - Revert. The mainstream view is that "Chromosome 2 thus presents very strong evidence in favour of the common descent of humans and other apes." Greensburger (talk) 04:02, 12 November 2010 (UTC)

RoquefortRaider (talk) 14:48, 2 September 2015 (UTC)

We can read this in this section: "This necessitates an implausible series of events, including the loss of both chimp centromeres when chromosomes 2A and 2B fused, and the rapid evolution of a new centromere to provide functionality to human chromosome 2." This statement is not backed by any peer-reviewed work and is, quite frankly, nothing more than creationist nonsense. It has no place in a serious article and should be deleted ASAP. Roquefort Raider

Wikipeedia is clear that creationism is fringe. Claiming that an (allegedly) unlikely event deserves an even more unlikely explanation such as creationism is not a scientific or mainstream viewpoint. This talk page is also not a forum to discuss creatonist ideas concerning human chromosome 2. We need to be very tight on sourcing everything and obviously with mainstream sources. This is worht reporting on the fringe noticeboard which is exsactly to prevent this kind of POV pushing. ♫ SqueakBox talk contribs 18:31, 2 September 2015 (UTC)

Disseminating "Fusion" across an existing population

At the end, the article suggests that a fusion event such as an 8/9 fusion could be disseminated across an existing population.

I find it very unlikely that post-fusion there would be significant mixing of the now genetically distinct populations.

Consider the Equine Species. Each member of the equine species has a different number of chromosomes.

Horses have 64 Chromosomes.

Donkeys have 62 Chromosomes.

Zebras have 32 or 46 Chromosomes.

When a horse and donkey crosses one gets a mule with 63 chromosomes. The first generation crossbred has a complete set of genes and is viable. However, the odd number of genes, as well as improperly matched gene pairs disrupts meiosis, and second generation offspring does not receive the full gene compliment and is not viable. Or, perhaps only a small fraction of the second generation offspring would receive the full genetic compliment to be viable leading to the novel major mutation to eventually die out. This helps ensure a stable gene compliment across a population.

The gene fusion likely occurred in a single family, possibly with a rapid succession of evolutionary changes. The new fused population then spread out in parallel with the existing hominid population. But rather than merging with the existing population, the chromosome fusion population developed independently, and eventually out competed and replaced the existing population.Keelec (talk) 19:36, 9 November 2010 (UTC)

"Genes" section

What's the point of the "Genes" section of the article? It seems to be just a random selection out of many. I don't detect any criteria. I presume these are not the Chr. 2 genes of "major importance" (by whatever definition). -R. S. Shaw (talk) 23:11, 30 June 2011 (UTC)

I'm sure many people can use it for some reason or another, even if it's not complete or a list of genes of major importance. Of course, the list can always be expanded or made more relevant. Besides, don't you think it's a tiny bit important to mention what genes are in the chromosome? It seems kind of silly to talk about a chromosome (whose sole purpose in existing is to carry genes!) without mentioning the genes it carries. --TAW (talk) 00:31, 1 July 2011 (UTC)

Neanderthals

Do we know if Neanderthals had a fused chromosome 2. Did it happen before the last common ansestor of Humans and neanderthals branched off — Preceding unsigned comment added by Jimmy saville (talk • contribs) 13:36, 4 February 2012 (UTC)

According to the article, A High-Coverage Genome Sequence from an Archaic Denisovan Individual Matthias Meyer Et Al, linked as the third footnote, Denisovans carried the 2A/2B fusion. From the data, the authors concluded that the Neanderthals also likely carried the mutation, and that it had occurred somewhat earlier in human evolution, although they did not present Neanderthal specific data.Keelec (talk) 21:08, 6 February 2014 (UTC)

Creationist propaganda

An ip anon inserted his or her creationist propaganda here a week ago, and all the edits since have been trying to clear it up. The article clearly requiresw more eyes as this isnt the first time. Well done for people trying to report and fix the issue. ♫ SqueakBox talk contribs 01:19, 3 September 2015 (UTC)

All members of Hominidae except humans, Neanderthals, and Denisovans

The first sentence of the Evolution section says All members of Hominidae except humans, Neanderthals, and Denisovans have 24 pairs of chromosomes. This is misleading. Modern humans, Neanderthals, and Denisovans are the only members of Hominidae known to have 23 pairs of chromosomes. However, we don't know when the transition occurred. Although H.heidelbergensis 750,000 years ago seems likely, for all we know H. habilis or even Australopithecus could have had 23 pairs of chromosomes. Zyxwv99 (talk) 18:27, 2 August 2017 (UTC)

Pseudogene

The ncbi link includes all the pseudogene's as well as normal functioning genes. Should Pseudogenes be included in the Wikipedia list also? Opinions please Leveni (talk) 10:44, 8 January 2021 (UTC)