Parthenogenesis is a phenomenon accompanying the in vitro oocyte culture. It is stimulated by a variety of physical and chemical factors which oocytes are facing in vitro. As a consequence of artificial activation, a few different types of parthenones can be formed. Commonly observed are homogenous haploid parthenogenones but also mosaic haploids and diploids can arise. The karyotype of parthenones is not stable and can undergo modifications during further development. Mammalian parthenones do not usually develop beyond the blastocyst stage. Up to now, only one experiment carried out on sheep parthenones has demonstrated their developmental competence up to the 26th day of gestation. Usually, most parthenones die shortly after activation because of damages caused by the activating factors and decreased developmental potential. Moreover, the rate of parthenogenetic development, compared to IVF embryos, is delayed. Since the mechanism of parthenogenesis in mammals still remains unclear, the problem needs further studies.