Fig. 3.

A schematic diagram showing the steps from fertilization and creation of the zygote to development of the blastocyst. When the latter is implanted within the uterus, normal fetal development may proceed. In the process of in vitro fertilization, the embryo develops to the blastocyst stage and may then be placed in the uterus for implantation to occur. Derivation of embryonic stem cell lines involves dissociation of the blastocyst and culture of the cells from the inner cell mass under special conditions.