individual’s personal genome can really be said to contain six billion base pairs. Identifying individual bases in a stretch of the genome requires a sensor that can detect the subnanometer-scale differences between the four base types. Scanning tunneling microscopy is one physical method that can visualize these tiny structures and their subtle distinctions. For reading millions or billions of bases, however, most sequencing techniques rely at some stage on chemistry. A method developed by Frederick Sanger in the 1970s became the workhorse of the HGP and is still the basis of most sequencing performed today. Sometimes described as sequencing by separation, the technique requires several rounds