Parthenogenesis

Parthenogenesis is a reproductive strategy that involves development of a female gamete 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. Parthenogenic species may be obligate or facultative. Parthenogenesis is sometimes considered to be an asexual form of reproduction; however, it may be more accurately described as an incomplete form of sexual reproduction, since offspring of parthenogenic species develop from gametes. Gametes are reproductive cells that result from meiosis in which a specialized cell with a double set of chromosomes undergoes two fissions of its nucleus. Meiosis gives rise to four gametes, or sex cells, which are haploid in that each possesses half the number of chromosomes of the original cell. Sometimes associated with arrhenotoky, thelytoky, and deuterotoky is pseudoarrhenotoky. Pseudoarrhenotoky is a nonparthenogenic form of reproduction that occurs in the hymenopteran superfamily Chalcidoidea and in some mites, Like arrhenotoky, pseudoarrhenotoky results in the production of haploid males. In this process, development begins as diploid organisms within fertilized eggs; however, as development progresses, males become haploid after the paternal contribution to the genome has been lost, eliminated, or deactivated.