Fig. 1.

Germline segregation strategies. (A) In animals that segregate their germline during embryogenesis, primordial germ cells (PGCs) are specified in the embryo. PGCs give rise exclusively to either male or female germline stem cells (GSCs), which both self-renew (as indicated by the curved arrows) and give rise to a constant supply of gametes. Gametes are highly specialized cells, but when they fuse at fertilization they create a totipotent zygote. (B) In animals that segregate their germline after embryogenesis, a multipotent progenitor is established in the embryo from which the germline is segregated after embryogenesis is completed. We propose that the red cells in both panels operate a conserved germline multipotency program.