Add Yahoo as a preferred source to see more of our stories on Google. A scientist examines a DNA (deoxyribonucleic acid) profile on a screen. Photograph by Tek Image, Science Photo Library Shakespeare ...

In a way, sequencing DNA is very simple: There's a molecule, you look at it, and you write down what you find. You'd think it would be easy—and, for any one letter in the sequence, it is. The problem ...