On Start the Week Andrew Marr traces the quest to decipher the human genome. The idea of a 'unit of heredity' first emerged at the end of the 19th century: cancer physician Siddhartha Mukherjee recounts the history of the gene and the latest research into genetic heredity and mutation. Giles Yeo looks at what genes can tell us about body weight, while Aarathi Prasad explores how India practises medicine - from cutting-edge science to traditional healing. The historian Emily Mayhew traces the medical breakthroughs that have emerged from the battlefield, from World War I to the conflict in Afghanistan.