We just combined a couple of them. Every now and then, chromosomes fuse. This fusion occurs as sperm and eggs develop, as pairs of chromosomes fold over each other and swap chunks of DNA. Sometimes two different chromosomes grab onto each other and then fail to separate. Scientists have observed both humans and mammals with fused chromosomes.
Chromosomes typically have distinctive stretches of DNA in their center and at their ends. This might seem like a fantastic mutation—something like a human and a horse being joined into a centaur. If humans and apes did indeed share a common ancestor, then it would make sense that two chromosomes fused in our ancestors. The rise of genome sequencing allowed them to test that hypothesis. The chimp genome team were able to match human chromosome two to two unfused chromosomes in the chimpanzee genome. What makes evolutionary biology such a fun subject to write about is that it does not stay still.
They were able to do so thanks to the publication earlier this year of the gorilla genome. A comparison of the human, chimpanzee, and gorilla genomes confirms that the ancestors of gorillas branched off from the ancestors of chimpanzees and humans about ten million years ago. Humans and chimpanzees then branched apart later. By comparing human chromosome two to the unfused versions in the chimpanzees and gorillas, Eichler and his colleagues reconstructed the chromosomes in the common ancestor of all three species:.
The bands correspond to segments of each chromosome. The hash marks represent regions of very unstable DNA. These areas, which are full of repeating sequences, are prone to accidentally getting duplicated, expanding the chromosome. It had picked up part of the green chromosome earlier than the common ancestor of us, chimpanzees, and gorillas. Three key events are illustrated here. First, the top of the green chromosome flipped another common type of mutation, called an inversion.
Then a chunk of yet another chromosome got stuck to the end of the green chromosome, marked here in pink. And then a new piece of DNA got stuck at the end of the green chromosome, known as StSat, and marked here as a yellow dot. The ancestors of gorillas then diverged from the ancestors of chimpanzees and humans.
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They underwent some ten million years of independent evolution, during which time a lot happened. For one thing, the cap on the green chromosome got duplicated and pasted onto other chromosomes, including the red one, and even on the other end of the green one itself. In the illustration below, the yellow and pink segments, along with the adjoining green segment, are represented by a brown oval.
Meanwhile, the ancestors of chimpanzees and humans were evolving. The two chromosomes continued to change, as shown here. A copy of StSat got glued to the end of the red chromosome, and then the pink and green segments at the top of the green chromosome got flipped. The chromosomes at the right of the figure show you what our two chromosomes looked like before they got fused. When the human and chimpanzee lineages split, each lineage inherited them. And in each lineage, they evolved in a different way. The caps on both the green and red chromosomes were duplicated massively and ended up on lots of other chromosomes.
The two chromosomes fused, and the cap was deleted, inclusing StSat. It could no longer spread around our genome, the way it did in chimpanzees and gorillas. This study is an important advance in our understanding of how human chromosomes evolved—a subject of medical significance, too, since the duplication of the DNA at the end of chromosomes can cause dangerous mutations that can cause genetic disorders. Plus, it is very cool to see how our chromosomes are, in fact, an ancient patchwork. It just so happens that I came across this paper by a very roundabout way—but an instructive one.
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The page is set up by an outfit called The Biologic Institute, which is promoting a new book by two of its employees that purports to reveal all the flaws in the evolutionary account of human beings. They linked to a post on a site run by the intelligent design clearinghouse, the Discovery Institute, which provided some details from the book. Matzke left several comments explaining why they were wrong, and what some of the evidence for human evolution actually is.
I found this deliciously ironic and had to jump in too. I pointed out that the site they linked to does not allow comments which is fairly typical of creationist web sites. So there was no other way to ask questions than to post them to Facebook. And my question concerned fused chromosomes.
The evidence from chromosomal fusion, for one, is strikingly ambiguous. Ergo, common descent. Nothing stands in the way of picturing a human population bottleneck accomplishing the spread of a fused chromosome 2 from part of an early human community to all of it. But the idea of such an event having occurred at all is itself far from sure.
The telomeric DNA parked in the middle of chromosome 2 is not a unique phenomenon. Other mammals have it too, across their own genomes. Of course, there's also the movie Independence Day. Hoaxes are the best explanation for computer-generated images of UFOs. What about alien abduction? See the extraordinary effects of sleep paralysis. For thousands of years, countless individuals from cultures around the world have reported what we now term as out of body experiences. Because it feels so real, it's interpreted as a literal separation of a mind or soul from the physical body.
Such an event appears to be strong evidence for a spirit world, afterlife, and even alternate dimensions in which other intelligent beings exist.
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Could the OBE really prove the existence of life after death? As a lucid dreamer I'm familiar with the out-of-body state. It all takes place inside the grand theater of your mind. Instead of projecting your awareness into a fanciful dreamworld as in a WILD you find yourself aware of the sleep paralysis which prevents you from acting our your dreams.
You're in a replica of your bedroom, floating above your "body". This is spurred by diminishing bodily sensations as you fall asleep physically. So convinced that the experience is real, out of body explorers have long tried to prove its validity by trying to obtain data from faraway locations. Unfortunately nothing definitive has emerged under the necessary scientific conditions to lend credence to the true OBE state.
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The Pyramids of Giza in Egypt really are something special. We still don't really know how the Egyptians built the largest pyramid of all, known as the Great Pyramid of Cheops or Khufu , some 5, years ago. Remember, this was even before the invention of the wheel. The Pyramid of Cheops is the size of a storey building and covers an area big enough to fit 10 football fields in it. More than 2 million stone blocks were used to make the pyramid, each weighing tons and cut from a distant limestone quarry on the other side of the Nile. Experts reckon it took , men some 20 years to complete.
Engineering feats aside, these structures are claimed by some to possess the unexplained phenomenon of Pyramid Power. In the s, a Czech radio engineer named Karel Drbal claimed that small pyramids of the same relative dimensions as the Great Pyramid on a , scale could sharpen razor blades. His explanation was that the pyramid shape focuses cosmic energy when precisely aligned on the north-south axis, which can renew the crystalline structure of steel. Despite the claims of Drbal and others, there is no scientific evidence that Pyramid Power exists. It is a cut and dry myth, presumably driven by the compelling nature of pyramids and their ancient, unexplained origins.
But as the Skeptic's Dictionary enthusiastically points out: "That almost anything in the universe can be found to have interesting mathematical proportions or be related to several interesting mathematical formulae is of little interest to pyramidiots. As the neurologist Terence Hines wrote: "Pyramid Power became quite a craze in the world of pseudoscience for a brief time in the mids.
The idea was that the pyramidal shape itself was magical and filled with a mysterious energy and power. In , Alter and Simmons showed that pyramid-shaped containers were no more effective than any other shape at preserving organic matter flowers or meat placed in them. Nor did putting dull razor blades in a pyramid-shaped holder restore them to sharpness. In , in the small Spanish village of Belmez, Maria Pereira claimed a human face spontaneously appeared on her cement kitchen floor. It wasn't long before she destroyed the floor and replaced it - and a new face promptly appeared.
More and more faces continued to appear on the floor of Pereira's kitchen, attracting thousands of visitors every day. Some were male, some female, some large, and some small. In time, she discovered that the house, built around , apparently stood above a graveyard used by the Romans, Spanish Muslims and then Medieval Christians. Paranormal fans suggest that the faces were manifested on the floor by telekinesis.
This notion was based on claim that the expressions on their faces used to change with the mood of Maria Pereira. For a long time, skeptics suspected that Maria Pereira painted the faces herself. But this didn't really add up - because she never benefited financially from all the attention. She lived a simple life in that same house and eventually died in It wasn't until recently that technology could explain this mystery.
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