The twentieth century history of genetics has a pleasing symmetry about it: it opened with the discovery of Mendel's work on the genetics of the garden pea and closed with the publication of the first draft sequence of the complete human genome. It was, of course, neatly bisected by Crick and Watson's publication in Nature of the structure of DNA. Despite a now famous photo call for a magazine, their momentous discovery remained largely hidden from the general public for some years: even the Nobel Prize took almost a decade to arrive. But we realize today that the pause was just an incubation period. Like a genetically manipulated virus, DNA has now escaped the laboratory and infected the whole world. We are in the midst of a pandemic.
Virus seems an apt metaphor: there is the same reproductive capacity, the same ability to lie dormant within the body politic and break out when least expected, the same disturbing tendency to mutate. Take, for example, the latest comic book hero to hit the screen, Spiderman. In the original Marvel stories it was the bite of a radioactive spider that started Peter Parker's mutation into the arachno-hero, but the film version addresses newer fears. In the new millennium the spider that bites Parker has, of course, been genetically manipulated. And such is our familiarity with the famous double helix that we are treated to a Hollywood view of the whole strange phenomenon—Parker's DNA twisting and turning, breaking and recombining into its new, hybrid form. The audience gets the point. What will have escaped most people, however, is a more subtle mutation: all of Parker's DNA is left-handed. I don't mean that it is Z-DNA; no, the nascent Spiderman's DNA is a left-handed version of B-DNA (see http://www.spiderman.sonypictures.com and see also http://www.lecb.ncifcrf.gov/~toms/ Leftyear2002.html). It is a mirror image of the real thing. We are in Looking-glass Land here, and Lewis Carroll would have loved it. “Perhaps Looking-glass milk isn't good to drink,” mused Alice. I wonder what she'd have thought about Looking-glass DNA.
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