The hope and promise of genetic engineering for all people born with genetic diseases-that a lifetime of treatments and medicines can be replaced with a one-time cure. It is not just sick people, however, who can benefit from genetic engineering. Every living thing carries genetic information in the nucleus of almost every cell in the body. Scientists say that genes are the words in the giant book of life written by deoxyribonucleic acid (DNA). This book makes reproduction possible, whether for bacteria or a plant or a human being. It determines how living things develop, what traits and characteristics they have, and what species of life they are.