The world experts in the fields of human gamete cytogenetics and the etiology of aneuploidy discuss the latest research in this volume. The frequency and distribution of abnormalities in human oocytes and sperm are explored, as are the effects of maternal and paternal ages. Research on basic mechanisms causing aneuploidy, such as decreased meiotic recombination, defective meiotic checkpoints, skewed X-chromosome inactivation, and biological aging are elaborated. With the advent of in vitro fertilization and intracytoplasmic sperm injection, there has been an explosion of research on the association of infertility with chromosome abnormalities in gametes. These are explored both for individuals with somatic chromosome abnormalities and for infertile patients who have a normal karyotype but still produce gametes with an increased frequency of cytogenetic abnormalities. The most recent research on meiotic abnormalities in these infertile patients is included. Since humans have such a devastating load of numerical chromosome abnormalities, environmental and lifestyle issues are discussed and related to mammalian model systems. This up-to-date and comprehensive volume will be a resource for geneticists, cell biologists, infertility experts, reproductive scientists, obstetricians, andrologists, and staff of assisted reproductive clinics.