The vast majority of the human population and most civilizations have depended on the productivity of plant-based agriculture for sustenance, vitality, and quality of life during the preceding five to fifteen millenia. During this time, and especially since the rediscovery of Gregor Mendel's principles of heredity in the late nineteenth century, the genetic content (genome) of crop plants has become a more important resource for crop management and production. The dynamic genomes of crop plants contain tens of thousands of genes that interact with themselves and the environment to determine the many traits affecting crop productivity. Gradually, humans have learned that the genomes of crop species and their relatives contain a range of genetic variation for many traits; how the genomes are transmitted from parent to progeny; a few of the myriad relationships among genomes, genes, the environment, and traits; some methods and mechanisms for maintaining or modifying...