FIGURE 1.

Primordial germ cells migration pathway. Zygote is totipotent. The blastomeres are pluripotent. Due to asynchronous division the initial population of blastomeres in the vegetative pole preserves their potency. Primordial germ cells are located first at the vegetative pole of blastocyst, then in the hypoblast (yolk sac) to avoid of differentiation signals and maintain the polypotency. After gastrulation the primordial germ cells migrate by amoeboid movement back to the embryo through the peritoneum to the dorsolateral gonadal ridges.