Fig. 1

Mammalian generation transmission by parental individuals to offspring individuals (I-to-I) and parental embryos to offspring embryos (E-to-E). a I-to-I transmission: gametogenesis is a long-term process highly associated with individual development and growth. PGCs, from which both oocytes and sperm originate, are established by the post-implantation stage. The subsequent oogenesis and spermatogenesis necessarily depend on fetal development and postnatal gonadal growth from birth until puberty. Gametogenesis ensures the creation of new individuals of the next generation of mammals, where genetic information is transmitted to next generation. b E-to-E transmission: gametogenesis is induced in vitro in ESCs to form functional oocytes and sperm. The entire process depends on in vivo fetal development and prepubertal growth. The induced oocytes and sperm develop into normal offspring embryos following IVF. The IVF offspring embryos are further used to derive ESCs, which can in turn undergo complete gametogenesis via a new round of in vitro germline induction