What can a microscopic worm teach us about sex? Dr. Barbara Meyer emphasizes the value of studying the model organism C. elegans, a roundworm which has two sexes, but with a twist: they are male and hermaphrodite. Dr. Meyer explains how a single gene acts as a 'master switch' to activate a series of additional genes, resulting in a biochemical cascade that leads the worm to become male or hermaphrodite. The surprising differences between male and hermaphrodite lifestyles are also discussed. From the Series:HHMI’s Understanding Biomedical Research Series