Stat: Four. That’s how many letters in the DNA alphabet make up every living thing. Story: How does genetic information transmit across generations? While trying to find out, scientists Craig Mello and Andrew Fire quite by accident made a discovery in 1998 that would earn them a Nobel Prize—and pave the way for the first drug to take on harmful genes. Pew’s Dan LeDuc talks with Mello about science’s surprises. Additional audio licensed for use by the Nobel Foundation. All rights reserved. © Nobel Media 2006