The entire cycle of germ cell differentiation and reprogramming for reproduction. PGCs are naturally produced from epiblast cells, which are generated from ICM. The PGCs migrate to the fetus and take up residence in the ovaries or testes, where they develop into oocytes or sperm, respectively. In vitro experiments, iPSCs, and ESCs could be differentiated to germ cells, which could then develop into blastocysts. Blastocysts could be developed to ESCs in vitro or body in vivo. The body naturally harbors germ cells, and somatic cells in the body could be reprogrammed to derive iPSCs. PSCs, pluripotent stem cells; PGCs, primordial germ cells; ICM, inner cell mass; iPSCs, induced pluripotent stem cells; ESCs, embryonic stem cells.