Disclosed is a method for constructing a nucleus-implanted egg, a parthenogenetic embryo and for producing a parthenogenetic mammal each having 2 haploid genome sets originating in mammalian ova, and provides methods of constructing a nucleus-implanted egg having a haploid genome set derived from primitive ovarian follicle egg (ng ovum) and a haploid genome set from MII phase (second meiosis metaphase) egg (fg ovum), a parthenogenetic embryo and a parthenogenetic mammal, including steps (1) introducing ng ovum into a nucleus-deleted deleted germinal vesicle stage (GV) egg, developing the obtained egg to MII phase by in vitro maturing and culturing to prepare a first nucleus-implanted egg, and (2) extracting MII phase chromosome from the first nucleus-implanted egg and introducing it into other fg ovum to prepare a second nucleus-implanted egg, wherein a ng or fg ovum from which an imprinted gene undergoing epigenetic modification during sperm generation is used.