Soon after Watson and Crick found that DNA is made up of four subunits, including one called cytosine ,scientists discovered a so-called fifth subunit: methylated cytosine. Experiments in the 1990s showed that methylated cytosine acts as a switch that can turn a gene on or off. But researchers had trouble distinguishing it from ordinary cytosine. Alexander Olek found an easy way to make it stand out, exposing relationships between the switch and disease. Olek also developed lab techniques for quickly scouring large volumes of DNA for the switch. His work made him a pioneer in “epigenetics,” which explores how environmental factors alter DNA. Olek, who dreams of helicoptering to a mountaintop to ski virgin snow, brings an adventuresome attitude to his work. At 19 he started his first enterprise, which looked for genetic features of diseases common in South America. While he was finishing his doctorate, Olek started Epigenomics in Berlin to advance his methylation work. With $35 million of investment capital, Epigenomics plans to market cancer detection tests that sense tumors’ methylation signals.