Genomic imprinting is a barrier to parthenogenesis in mammals.

Only mammals have relinquished parthenogenesis as a means of producing descendants. Bi-parental reproduction is necessary due to parent-specific epigenetic modification of the genome during gametogenesis, which leads to non-equivalent expression of imprinted genes from the maternal and paternal alleles. However, a series of our work showed that alteration of maternal imprinting by oocyte reconstruction using non-growing oocytes, together with deletion of the H19 gene provide appropriate expression of imprinted genes from the maternal genome. The resulting ng (non-growing)/fg (fully-grown) parthenogenic embryos were developed to term. Here, we discuss how the parthenogenetic embryos survived as normal individuals. 2006 S. Karger AG, Basel.