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1 " Our brains contain one hundred billion nerve cells (neurons). Each neuron makes links with ten thousand other neurons to form an incredible three dimensional grid. This grid therefore contains a thousand trillion connections - that's 1,000,000,000,000,000 (a quadrillion). It's hard to imagine this, so let's visualise each connection as a disc that's 1mm thick. Stack up the quadrillion discs on top of each other and they will reach the sun (which is ninety-three million miles from the earth) and back, three times over. "
― Nessa Carey , The Epigenetics Revolution
2 " Whenever we describe the genome we talk about it in very two-dimensional terms, almost like a railway track. Peter Fraser’s laboratory at the Babraham Institute outside Cambridge has published some extraordinary work showing it’s probably nothing like this at all. He works on the genes that code for the proteins required to make haemoglobin, the pigment in red blood cells that carries oxygen all around the body. There are a number of different proteins needed to create the final pigment, and they lie on different chromosomes. Doctor Fraser has shown that in cells that produce large amounts of haemoglobin, these chromosome regions become floppy and loop out like tentacles sticking out of the body of an octopus. These floppy regions mingle together in a small area of the cell nucleus, waving about until they can find each other. By doing this, there is an increased chance that all the proteins needed to create the functional haemoglobin pigment will be expressed together at the same time2 "
3 " But DNA isn’t really like that. It’s more like a script. Think of Romeo and Juliet, for example. In 1936 George Cukor directed Leslie Howard and Norma Shearer in a film version. Sixty years later Baz Luhrmann directed Leonardo DiCaprio and Claire Danes in another movie version of this play. Both productions used Shakespeare’s script, yet the two movies are entirely different. Identical starting points, different outcomes. "
4 " Sometimes the greatest scientific breakthroughs happen because someone ignores the prevailing pessimism. "
5 " It’s not just humans who have trisomies of the sex chromosomes. One day you may be happily amazing your friends with your confident statement that their tortoiseshell cat is female when they deflate you by telling you that their pet has been sexed by the vet and is actually a Tom. At this point, smile smugly and then say ‘Oh, in that case he’s karyotypically abnormal. He has an XXY karyotype, rather than XY’. And if you’re feeling particularly mean, you can tell them that Tom is infertile. That should shut them up. "
6 " In 2002 scientists demonstrated beautifully just how random the process of X inactivation really is, by cloning a calico cat. They took cells from an adult female cat, and carried out the standard (but still fiendishly tricky) process of cloning. To do this, they removed the nucleus from the adult cat cell and put it into a cat egg whose own chromosomes they’d removed. This egg was implanted into a surrogate cat mother, and a lively and beautiful female kitten was born. And she didn’t look anything like the genetically identical cat of which she was a clone.18 "
― Nessa Carey , Junk DNA: A Journey Through the Dark Matter of the Genome
7 " Imagine Spider-Man is standing in a set position and needs to get something. He throws a web at the thing he wants, and then drags it to him. Now imagine that a very tiny Spider-Man is standing at one end of a cell. He throws a web at the chromosome he wants, the web attaches, and he pulls the chromosome to his end of the cell. A tiny Spider-Man clone does the same thing at the opposite end of the cell for the other chromosome in the matching pair. "
8 " Children who eat breakfast are statistically more likely to do well at school than children who skip breakfast. "
9 " You could make iPS cells by introducing just four genes into a differentiated cell. "
10 " Incredibly, the human body produces about 2 million red blood cells every second. "
11 " It also showed that the only real block to bi-maternal reproduction is the DNA methylation pattern at key genes. It disproved a previous hypothesis that sperm were required because the sperm themselves carried certain necessary accessory factors such as particular proteins or RNA molecules required to kick-start development properly.16 "
12 " More long non-coding RNAs are expressed in the brain than any other tissue (with the possible exception of the testes).26 Some have been conserved from birds to humans, with expression patterns that occur in the same regions and at the same developmental stages. These "
13 " Simple organisms like bacteria tend more to the Airfix way of life. Their genes are fairly set, coding for just one protein. The more complex an organism becomes, the more the genome begins to resemble LEGO, with a much greater degree of flexibility in how the components are used. And when we think how extraordinary we humans are, it seems reasonable to say, in a nod to certain movie, that at the genetic level 'everything is awesome'. "
― Nessa Carey
14 " why are males viable if they only have half as many X chromosome genes as females? The answer is that expression of X-linked genes is actually pretty much the same in males and females, despite the different number of chromosomes, a phenomenon called dosage compensation. The XY system of sex determination doesn’t exist in other animal classes so X chromosome dosage compensation is limited to placental mammals. "
15 " It’s incredible to think that mammalian cells carry about 20,000 genes, and yet it only takes four to turn a fully differentiated cell into something that is pluripotent. With just four genes Professor Yamanaka was able to push the ball right from the bottom of one of Waddington’s troughs, all the way back up to the top of the landscape. "
16 " Only 2 per cent of our genome codes for proteins. A massive 42 per cent is composed of retrotransposons. These are very odd sequences of DNA, which probably originated from viruses in our evolutionary past. Some retrotransposons are transcribed to produce RNA and this can affect the expression of neighbouring genes. This can have serious consequences for cells. If it drives up expression of genes that cause cells to proliferate too aggressively, for example, this may nudge cells towards becoming cancerous. "
17 " While a role for DNA methylation may not have come as a shock, it may be surprising to learn that it is often not the gene body that is methylated. The part of the gene that codes for protein is epigenetically broadly the same when we compare the maternal and paternal copies of the chromosome. It’s the region of the chromosome that controls the expression of the gene that is differently methylated between the two genomes. "
18 " If DNA is black-to-white with perhaps a few shades of grey depending on the level of methylation, histone modifications are glorious technicolour. "
19 " These experiments showed that there was a region on the X chromosome that was vitally important for X inactivation. This region was dubbed the X Inactivation Centre. In 1991 a group from Hunt Willard’s lab at Stanford University in California showed that the X Inactivation Centre contained a gene that they called Xist, after X-inactive (Xi) specific transcript10. This gene was only expressed from the inactive X chromosome, not from the active one. Because the gene was only expressed from one of the two X chromosomes, this made it an attractive candidate as the controller of X inactivation, where two identical chromosomes behave non-identically. "
20 " sometimes the most extraordinary biology lies hidden in the most apparently mundane of assumptions. "
