Who or what is the preembryo?

... The moral status -- and specifically the controversial issue of personhood -- is related to attainment of developmental individuality... This contrasts with the view that holds that personhood occurs earlier, at the point of genetic uniqueness. I believe that an embryo that has developed to the point where it can be one individual and one individual only, differs in moral status from a preembryo that has not, even if in many cases we may choose to treat them similarly... In view of the conviction that the preembryo is not yet a person and that its statistical potential for becoming such is small, it is not clear that nontherapeutic experiments can be excluded in principle. However, because the preembryo does have intrinsic potential...the preembryo should be treated as a person... Any exceptions from the prima facie duty to treat the preembryo as a person should be based on criteria established at the national level....