A reproductive strategy that involves the development of a female (rarely a male) gamete (sex cell) without fertilization. It occurs commonly among lower plants and invertebrate animals and rarely among higher vertebrates An egg produced parthenogenetically may be either haploid or diploid (i.e., with a paired set of chromosomes). Parthenogenic species may be obligate (that is, incapable of sexual reproduction) or facultative (that is, capable of switching between parthenogenesis and sexual reproduction depending upon environmental conditions). The term parthenogenesis is taken from the Greek words parthenos, meaning “virgin,” and genesis, meaning “origin.”