The molecule of life DNA arises to say that its structure and components are the generators of the diversity of life that serves the continuity. Without changes in DNA sequences, there is no variation, and without variation, there are no changes that can occur in phenotypic variability, no adaptation to environmental changes, and no evolution. This book focuses on the fundamental aspects and machinery of storing, replicating, transmitting, and decoding information by DNA molecules. These processes are the basis for chromosome mapping analysis and genetic recombination manifested essentially in this book by molecular genetic investigations of bacteria and the viruses that invade them. In addition, the characteristics of RNA coronaviruses and their replication are presented.