The significance of parthenogenetic virgin mothers in bonnethead sharks and mice

Two astonishing virgin births in quick succession have raised interest in parthenogenesis in cartilaginous sharks and mammals. These were believed to be exceptions until numerous female bonnethead (hammerhead) sharks were found be giving birth at the Henry Doorly Zoo in Nebraska, despite the prolonged absence of male sharks. The birth of a shark pup led to suggestions that spermatozoa from a previous coitus had persisted in the female tract of its mother and fertilized one of her eggs some months later. These proved to be incorrect because the female had been isolated for several years whereas spermatozoa persisted in the female tract for approximately 6 months. Molecular investigations into the pup's DNA failed to find any paternal contribution and proved the pup to be descended from its mother only. Just before this discovery, a study in mice had revealed that parthenogenesis could be induced by overcoming damage to embryonic development that is normally caused by gene imprinting. This was done by fusing two mouse oocytes and then inserting Igf2 into the parthenogenotes, which led to the birth of several parthenogenetic offspring. Modifying epigenesis had thus opened pathways to full-term parthenogenetic development. The birth of these parthenogenotes fulfils the attempts of earlier scientists to invoke parthenogenesis in experimental animals.