The 20th century opened with the rediscovery of Gregor Mendel's work on inheritance. By the close of the century, the human genome was almost fully sequenced. Dr. Lander takes us on a tour of this remarkable genetic century, demonstrating how rapid advances in DNA sequencing technologies and information science have been essential in accelerating the pace of whole-genome sequencing of different organisms. He also discusses the total number of human genes and other features of the human genome. A comparison of the human genome with the recently completed mouse genome reveals remarkable similarities, as well as some important evolutionary differences.