In this book, the authors present current research in the study of germ cells. Topics include the molecular signature and sub-cellular machinery of metazoan gametogenic stem cells; recent advances in understanding germ cell-specific organelles and their functions; low-dose radiation induces apoptosis in male germ cells of mice and attenuates it in type 1 diabetes rats; oocyte nuclear structure during mammalian oogenesis; and chromatoid body assembling and nuclear cycles.