Parthenogenesis

Parthenogenesis (Greek παρθενος, "virgin", + γενεσις, "birth") means the growth and development of an embryo or seed without fertilization by a male.

Parthenogenesis occurs naturally in some lower plants (there called agamospermy), invertebrates (e.g. water fleas, aphids) and some vertebrates (e.g., lizards, salamanders some fish, and even turkeys), where it can be used for reproduction in the absence of males.

Animals that can reproduce through parthenogenesis are more likely to settle in isolated habitats like oceanic islands, as only a single (female) member of the species has to reach the habitat.

The alteration between parthenogenesis and sexual reproduction is called heterogamy.

Parthenogenesis is also seen as a possible way to clone mammals, with the emphasis on human cloning.

Gynogenesis

A special form of parthenogenesis is gynogenesis. Species that reproduce by gynogenesis (e.g., some salamanders of the genus Ambystoma) can perform only parthenogenesis, and consist entirely of females. They do, however, have sexual contact with the males of closely related species. The sperm from these males is not used to fertilize the egg; it just stimulates egg development without any exchange of genetic material. It is believed that the success of those salamanders is due to the rare (perhaps only one mating out of a million) actual fertilization of eggs by a male, introducing new material to the gene pool.