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                                                Cell nucleus - illustration
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                                                Illustration courtesy of the National Library of Medicine. 
 
Genetics Home Reference. [Internet] Bethesda (MD): National Library of Medicine (US);  [published: October 31, 2007; cited November 1, 2007] Cells and DNA. 
 
Available from http://ghr.nlm.nih.gov/handbook/illustrations  
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