I have a question about this fusion that I still don’t understand, It’s worth mentioning that I have searched for the answer to this question without luck, I must be looking in the wrong places so I thought I would ask the people who know, and that’s you.

First of all, I’m totally on board with the basics of this fusion. I know Chromosomes have telomeres on each end, with a centromere in the middle, and two of these fusing end to end would result in telomeres in the middle with two centromeres. So when the finding was published of a head to head fusion that matches with the ape chromosomes of 2p and 2q with all the centromeres and telomeres in the right place; it should be convincing even for Kent Hovind, but alas, that guy is something else.

Though the part I don’t understand is this, humans have a total of 46 chromosomes, while the great apes have a total of 48? How can the fusion of two individual chromosomes which join to form one, get us to the conclusion of 46 chromosomes instead of what one would think should be 47?

Before I get jumped on for posting in such ignorance, I am aware that chromosomes come in pairs, 23 pairs in humans and 24 pairs in apes, so it would seem to make sense that the equation 48-1 = 47 would be replaced by 24-1 =23 (46) and everything would be fine. Though the fusion that was described to be found was the fusion of two individual chromosomes, so 2 of the 48, not 2 of the 24. Ken miller describes pretty clearly that this fusion would have 2 vestigial centromeres and 2 fused telomeres in the middle which I would assume to be the new centromere, so as Ken describes this fusion site, he can only be describing the fusion of two individual chromosomes, namely 2p and 2q in the ape line, each with a telomere on either end and a single centromere in the middle.

I get the feeling there actually is a second fusion site that I simply hadn’t heard about. Or since the discovered fusion gets us only to 47 chromosomes, there is a yet undiscovered second fusion, somewhere in another human chromosome.

And since the chromosome 2 matches only with 2p and 2q (Ape) and not with any of the other ape chromosomes (correct me if I’m wrong) it seems Chromosome 2 (Human) could only be the result of a fusion between these two individuals (2p, 2q), which means, once they fused, that brings the chromosome count to 47, and no remnants of any fusions of other ape chromosomes are found, at least not in chromosome 2 (Human).

My question ironically boils down to this, how can 1+1=2 when 1+1 should equal 1? Appreciate any response. If it turns out I overlooked something very obvious, I’ll see if I can get this thread renamed to... Call this guy an idiot thread.

Deleted.

PZ Myers gives a pretty good explanation in this article:

http://scienceblogs.com/pharyngula/2006 ... -genetics/

What almost certainly happened is that a balanced translocation occurred so that, as you say, a subpopulation had 47 chromosomes. That is to say they would have a copy of chromosome A and of chromosome B that they inherited from one parent, and single chromosome consisting of a fusion of A and B from the other parent, whereas the rest of the population would have two copies each of A and B as separate chromosomes. Eventually, however, examples of the two, unfused chromosomes disappeared and everyone in the human line only had two copies of the fused chromosome, bringing the number down to 46.

Shrunk, thanks heaps for your response, that clears that up nicely. I can't believe I didn't think of this, thanks. Also that link was very informative, cheers for that, always good to see Casey Luskins exploits

Though a quick follow up question if you have the time just so I can understand this more clearly, this fusion occurred between 2 individual chromosomes from different pairs right? It wasn't just one pair that fused together? I know the chromosomes are described as 2p for the short arm and 2q for the long arm, but as I've been trying to understand this I've come across it being said that chromosome 2A and 2B fused, so I'm assuming there exists two copies of 2A and two copies of 2B in apes? And if that's the case, how does one know which arm is being spoken of when only 2q or 2p is mentioned in the literature? Since it could be the short or long arm from either of these pairs.

I'm not sure I really understand your question. I'm pretty sure the unfused chromosomes in our ape relatives go by different numbers, and not #2. You might want to read this series of articles by Carl Zimmer. Even if it doesn't answer your question, it recounts some more very amusing antics from Casey Luskin and his creationist friends:

http://blogs.discovermagazine.com/loom/ ... vKWA6PD-71

Dawkins Fanboy wrote:Shrunk, thanks heaps for your response, that clears that up nicely. I can't believe I didn't think of this, thanks. Also that link was very informative, cheers for that, always good to see Casey Luskins exploits

Though a quick follow up question if you have the time just so I can understand this more clearly, this fusion occurred between 2 individual chromosomes from different pairs right? It wasn't just one pair that fused together? I know the chromosomes are described as 2p for the short arm and 2q for the long arm, but as I've been trying to understand this I've come across it being said that chromosome 2A and 2B fused, so I'm assuming there exists two copies of 2A and two copies of 2B in apes? And if that's the case, how does one know which arm is being spoken of when only 2q or 2p is mentioned in the literature? Since it could be the short or long arm from either of these pairs.

I'm no expert here, I'm going by the Wikipedia articles on chromosomes (the section on human chromosomes) and the chimpanzee genome project. Yes, the fusion was between 2 individual chromosomes from different pairs (it presumably happened in a sex cell, either an ovum or a sperm cell, which only have one of each pair of chromosomes). The 46 human chromosomes are only numbered from 1 to 22 (one number for each pair), with the pair of sex chromosomes called X and Y. It would have been simplest to number the chimpanzee pairs of chromosomes from 1 to 23 (plus the sex chromosomes), but if they had been numbered that way, most of the numbers would not have matched with the corresponding human pair; they would have been one out, which would have been a nuisance. So instead the chimpanzee chromosome pairs are numbered like the human chromosome pairs from 1 to 22, but the two chimp pairs which match the single human pair numbered 2, are numbered 2A and 2B. As you say, most of a chimp's cells (excluding the sex cells) will have 2 copies each of 2A and 2B.

I think the p and q names for long and short arms refer only to the point in cell division when the chromosome pairs become condensed and cross over, as described in the Wikipedia chromosome article here, I don't think it's about the bits of human chromosome 2 which come from different chimp chromosomes, but I could be confused:

Wikipedia wrote:Metaphase chromatin and division
See also: mitosis and meiosis

In the early stages of mitosis or meiosis (cell division), the chromatin strands become more and more condensed. They cease to function as accessible genetic material (transcription stops) and become a compact transportable form. This compact form makes the individual chromosomes visible, and they form the classic four arm structure, a pair of sister chromatids attached to each other at the centromere. The shorter arms are called p arms (from the French petit, small) and the longer arms are called q arms (q follows p in the Latin alphabet; q-g "grande"; alternatively it is sometimes said q is short for queue meaning tail in French[19]). This is the only natural context in which individual chromosomes are visible with an optical microscope.

Well, there you go. I was wrong.