100 Fixing the Calendar 1582


  Unraveling the Double Helix 1953



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76  Unraveling the Double Helix 1953 
THE OUTER EDGE of a vast, largely unmapped frontier looks a lot like a field in Scotland. The frontier is the human genome, and browsing in that field is a sheep who, for all she can tell, is like any other. The truth is she's exactly like another sheep--the one who provided the mammary cells from which she was cloned--and that's what makes Dolly different. She was created in a lab supported by a biotechnology company that plans to manufacture animals able to secrete drugs in their milk. Is this what James Watson and Francis Crick had in mind? 

Before even a rough topography existed, the presence of deoxyribonucleic acid in the nucleus of every living cell had been confirmed in 1869 by Swiss physician Friedrich Miescher. But science believed protein, not DNA, controlled heredity until Martha Chase and Alfred Hershey proved otherwise in 1952, setting off a race to say how DNA functions, to know what makes us who we are. 



Crick and Watson, who never experimented with DNA themselves, began building models of what they thought was the acid's molecular structure. On February 21, 1953, Watson, then 24, noticed the similar shape of the two complementary pairs of basic molecules that make up DNA, requiring two helices to wrap around its core, a revelation that also suggested how DNA might replicate itself. Knowing DNA's design would eventually lead to the identification of specific genes and their functions. 



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