Book excerpt: Genes - we all have them and we're all affected by them, often in unknown ways. Whether directly inherited or modified by our environment, genes control or significantly influence almost every aspect of our lives, from the success of our conception and the development of our sexual characteristics, to the colour of our skin, hair, and eyes; our height and weight; our health; and, unfortunately, an untold number of diseases. For many, the first time that genetics truly matters to them is in a doctor's office as they learn about a condition that may affect them, their unborn children, or even their wider family. Yet from the first laborious survey of the human genome twenty years ago to the commercial machines that now sequence 6,000 genomes per year, a revolution is taking place in medicine. Navigating this world of heartbreaking uncertainties, tantalising possibilities, and thorny questions of morality is Professor Edwin Kirk, a rare doctor who works both in the lab and with patients, and who has over two decades of experience. In The Genes That Make Us, he explains everything you need to know with clarity, insight, and great humanity.