Should the potential to produce a live birth form part of the biological definition of a human embryo?
Animal models have demonstrated that SCNT blastocysts have the potential to implant and develop to a live birth (Wilmut et al., 1997). It is therefore reasonable to assume that human SCNT blastocysts also have the potential to develop into a viable individual if placed within the correct environment. It has been demonstrated that transferring viable blastomeres from developmentally slow preimplantation embryos into an empty zona pellucida produces an aggregate preimplantation structure that can develop to the blastocyst stage, from which human embryonic stem cells can be derived (Alikani and Willadsen, 2002). Although it remains to be tested whether such aggregate blastocysts (reproductive technique 6) can implant and form a viable pregnancy, it is theoretically feasible. In the mouse model, significant progress has been made in the generation of gametes from embryonic stem cells (Hubner et al., 2003; Toyooka et al., 2003; Geijsen et al., 2004; Lacham-Kaplan et al., 2005). The generati
