# Parthenogenesis

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{{Short description|Asexual reproduction without fertilization}}
{{Redirect|Agamic|other uses|Agama (disambiguation){{!}}Agama}}
{{Use dmy dates|date=November 2024}}
[[File:Cnemidophorus-ThreeSpecies.jpg|thumb|280px|right|The asexual, all-female whiptail species ''[Aspidoscelis neomexicanus](/source/Aspidoscelis_neomexicanus)'' (center), which reproduces via parthenogenesis, is shown flanked by two sexual species having males, ''[A. inornatus](/source/Aspidoscelis_inornatus)'' (left) and ''[A. tigris](/source/Aspidoscelis_tigris)'' (right), which naturally hybridized to form ''A. neomexicanus''.]]

'''Parthenogenesis''' ({{IPAc-en|ˌ|p|ɑːr|θ|ᵻ|n|oʊ|ˈ|dʒ|ɛ|n|ᵻ|s|ᵻ|s|,_|-|θ|ᵻ|n|ə|-}};{{refn|{{MerriamWebsterDictionary|parthenogenesis}} }}{{refn|{{cite encyclopedia |title=parthenogenesis |department=English definition |dictionary=Oxford Dictionary [OxfordDictionaries.com](/source/OxfordDictionaries.com) |url=https://www.oxforddictionaries.com/definition/english/parthenogenesis |access-date=2016-01-20 |archive-url=https://web.archive.org/web/20120912090205/http://oxforddictionaries.com/definition/english/parthenogenesis |archive-date=12 September 2012 }} }} from the Greek {{langx|grc|{{math|παρθένος}}|translit=parthénos|lit=virgin|label=none}} + {{langx|grc|{{math|γένεσις}}|translit=génesis|lit=creation|label=none}}<ref>{{cite encyclopedia |editor1=Liddell |editor2=Scott |editor3=Jones |year=1940 |title={{math|γένεσις}} A.II |dictionary=A Greek-English Lexicon |place=Oxford, UK |publisher=Clarendon Press |url=https://www.perseus.tufts.edu/hopper/text?doc=Perseus:text:1999.04.0057:entry%3Dge/nesis |via=''Perseus'' / [Tufts U.](/source/Tufts_University), Medford & Somerville, MA }} ''q.v.''.</ref>) is a natural form of [asexual reproduction](/source/asexual_reproduction) in which the [embryo](/source/embryo) develops directly without need for [fertilization](/source/fertilization). In [animal](/source/animal)s, parthenogenesis means the development of an embryo from an unfertilized [egg cell](/source/Gametophyte). In [plant](/source/plant)s, parthenogenesis is a component process of [apomixis](/source/apomixis). In [algae](/source/algae), parthenogenesis can mean the development of an embryo from either an individual sperm or an individual egg.

Parthenogenesis occurs naturally in some [invertebrate](/source/invertebrate) animal species (including [nematodes](/source/nematodes), some [tardigrade](/source/tardigrade)s, [water flea](/source/water_flea)s, some [scorpion](/source/scorpion)s, [aphid](/source/aphid)s, some mites, some [bee](/source/bee)s, some [Phasmatodea](/source/Phasmatodea), and [parasitic wasp](/source/parasitic_wasp)s), a few [vertebrate](/source/vertebrate)s, such as some [fish](/source/fish), [amphibians](/source/amphibians), [reptile](/source/reptile)s,<ref name="Halliday-1986">{{cite book |last=Halliday |first=Tim R. |editor=Kraig Adler |title=Reptiles & Amphibians |publisher=Torstar Books |year=1986 |page=101 |isbn=978-0-920269-81-7}}</ref><ref>{{cite news
 |title=Scientists discover unknown lizard species at lunch buffet |first=Brian |last=Walker |url=http://www.cnn.com/2010/LIVING/11/10/lizard.lunch.discovery/ |publisher=CNN |access-date=2010-11-11 |date=2010-11-11}}</ref><ref>{{cite journal |last1=Allen |first1=L. |last2=Sanders |first2=K.L. |last3=Thomson |first3=V.A. |date=February 2018 |title=Molecular evidence for the first records of facultative parthenogenesis in elapid snakes |journal=Royal Society Open Science |volume=5 |issue=2 |article-number=171901 |doi=10.1098/rsos.171901  |doi-access=free|pmc=5830781 |pmid=29515892 |bibcode=2018RSOS....571901A}}</ref> and [bird](/source/bird)s,<ref>{{cite report |last=Savage |first=Thomas F. |date=11 February 2008 |orig-date=12 September 2005 |title=A guide to the recognition of parthenogenesis in incubated turkey eggs |series=Department of Animal Sciences |publisher=[Oregon State University](/source/Oregon_State_University) |url=http://oregonstate.edu/instruct/ans-tparth/index.html |archive-url=https://web.archive.org/web/20120716235633/http://oregonstate.edu/instruct/ans-tparth/index.html |archive-date=2012-07-16}}</ref><ref name="Ryder-2021"/><ref>{{cite journal |last1=Ramachandran |first1=R. |last2=Nascimento dos Santos |first2=M. |last3=Parker |first3=H.M. |last4=McDaniel |first4=C.D. |date=September 2018 |title=Parental sex effect of parthenogenesis on progeny production and performance of Chinese Painted Quail (''Coturnix chinensis'') |journal=Theriogenology |volume=118 |pages=96–102 |doi=10.1016/j.theriogenology.2018.05.027 |doi-access=free |pmid=29886358 |s2cid=47008147}}</ref> and some plants and [algae](/source/algae). It has been induced artificially in several animal species that naturally reproduce through sex, including fish, amphibians, and mice.<ref name="Booth-2010">{{cite journal |last1=Booth |first1=W. |last2=Johnson |first2=D.H. |last3=Moore |first3=S. |last4=Schal |first4=C. |last5=Vargo |first5=E.L. |year=2010 |title=Evidence for viable, non-clonal but fatherless boa constrictors |journal=[Biology Letters](/source/Biology_Letters) |volume=7 |issue=2 |pages=253–256 |pmid=21047849 |pmc=3061174 |doi=10.1098/rsbl.2010.0793}}</ref><ref name="Wei-2022">{{cite journal |last1=Wei |first1=Y. |last2=Yang |first2=C.R. |last3=Zhao |first3=Z.A. |date=7 March 2022 |title=Viable offspring derived from single unfertilized mammalian oocytes |journal=PNAS |volume=119 |issue=12 |article-number=e2115248119 |doi=10.1073/pnas.2115248119 |doi-access=free |pmid=35254875 |pmc=8944925 |bibcode=2022PNAS..11915248W}}</ref>

Normal egg cells form in the process of [meiosis](/source/meiosis) and are [haploid](/source/haploid), with half as many [chromosome](/source/chromosome)s as their mother's body cells. Haploid individuals, however, are usually non-viable, and parthenogenetic offspring usually have the [diploid](/source/diploid) chromosome number. Depending on the mechanism involved in restoring the diploid number of chromosomes, parthenogenetic offspring may have anything between all and half of the mother's [allele](/source/allele)s. In some types of parthenogenesis, the offspring that have all of the mother's genetic material are called full [clones](/source/Cloning) and those having only half are called half clones. Full clones are usually formed without meiosis. If meiosis occurs, the offspring get only a fraction of the mother's alleles, since [crossing over](/source/Chromosomal_crossover) of [DNA](/source/DNA) takes place during meiosis, creating variation.

Parthenogenetic offspring in species that use either the [XY](/source/XY_sex-determination_system) or the [X0](/source/X0_sex-determination_system) sex-determination system have two X chromosomes and are female. In species that use the [ZW sex-determination system](/source/ZW_sex-determination_system), they have either two Z chromosomes (male) or two W chromosomes (mostly non-viable but rarely a female), or they could have one Z and one W chromosome (female).

== Life history types ==

{{Further|Origin and function of meiosis}}

[[File:Parthkomodo.jpg|thumb|A young [Komodo dragon](/source/Komodo_dragon), ''Varanus komodoensis'', produced through parthenogenesis. Komodo dragons can produce offspring through both sexual reproduction and parthenogenesis.]]

Some species reproduce exclusively by parthenogenesis (such as the [bdelloid rotifers](/source/Bdelloidea)), while others can switch between sexual reproduction and parthenogenesis. This is called facultative parthenogenesis (other terms are cyclical parthenogenesis, heterogamy<ref>{{cite book |publisher=Walter de Gruyter |isbn=978-3-11-010661-9 |last=Scott |first=Thomas |title=Concise encyclopedia biology |year=1996 |url-access=registration |url=https://archive.org/details/conciseencyclope00scot}}</ref><ref>{{cite journal |volume=52 |issue=3 |pages=219–225 |last=Poinar |first=George O Jr |author2=Trevor A Jackson |author3=Nigel L Bell |author4=Mohd B-asri Wahid |title=''Elaeolenchus parthenonema'' n. g., n. sp. (Nematoda: Sphaerularioidea: Anandranematidae n. fam.) parasitic in the palm-pollinating weevil ''Elaeidobius kamerunicus'' Faust, with a phylogenetic synopsis of the Sphaerularioidea Lubbock, 1861 |journal=Systematic Parasitology |date=July 2002 |pmid=12075153 |doi=10.1023/A:1015741820235 |s2cid=6405965}}</ref> or heterogony<ref name="White-1984">{{cite journal |doi=10.1080/11250008409439455 |volume=51 |issue=1–2 |pages=1–23 |last=White |first=Michael J.D. |title=Chromosomal mechanisms in animal reproduction |journal=[Bolletino di Zoologia](/source/Bolletino_di_Zoologia) |year=1984}}</ref><ref name="Pujade-Villar-2001">{{cite journal |first1=Juli |last1=Pujade-Villar |first2=D. |last2=Bellido |first3=G. |last3=Segu |first4=George |last4=Melika |year=2001 |title=Current state of knowledge of heterogony in Cynipidae (Hymenoptera, Cynipoidea) |journal=Sessio Conjunta DEntomologia ICHNSCL |volume=11 |issue=1999 |pages= 87–107}}</ref>). The switch between sexuality and parthenogenesis in such species may be triggered by the season ([aphid](/source/aphid), some [gall wasps](/source/gall_wasps)), or by a lack of males or by conditions that favour rapid population growth ([rotifers](/source/rotifers) and [cladocerans](/source/cladocerans) like ''[Daphnia](/source/Daphnia)''). In these species, asexual reproduction occurs either in summer (aphids) or as long as conditions are favourable. This is because in asexual reproduction, a successful genotype can spread quickly without being modified by sex or wasting resources on male offspring who will not give birth. Some species can produce both sexually and through parthenogenesis, and offspring in the same clutch of a species of tropical lizard can be a mix of sexually produced offspring and parthenogenically produced offspring.<ref name="Kratochvíl-2020">{{cite journal |last1=Kratochvíl |first1=Lukáš |last2=Vukić |first2=Jasna |last3=Červenka |first3=Jan |last4=Kubička |first4=Lukáš |last5=Johnson Pokorná |first5=Martina |last6=Kukačková |first6=Dominika |last7=Rovatsos |first7=Michail |last8=Piálek |first8=Lubomír |display-authors=6 |date=November 2020 |title=Mixed-sex offspring produced via cryptic parthenogenesis in a lizard |journal=[Molecular Ecology](/source/Molecular_Ecology_(journal)) |volume=29 |issue=21 |pages=4118–4127 |doi=10.1111/mec.15617 |pmid=32881125 |bibcode=2020MolEc..29.4118K |s2cid=221474843 |url=https://onlinelibrary.wiley.com/doi/10.1111/mec.15617 |url-access=subscription}}</ref> In California condors, facultative parthenogenesis can occur even when a male is present and available for a female to breed with.<ref>{{cite journal |last1=Ryder |first1=Oliver A |last2=Thomas |first2=Steven |last3=Judson |first3=Jessica Martin |last4=Romanov |first4=Michael N. |last5=Dandekar |first5=Sugandha |last6=Papp |first6=Jeanette C. |last7=Sidak-Loftis |first7=Lindsay C. |last8=Walker |first8=Kelli |last9=Stalis |first9=Ilse H. |last10=Mace |first10=Michael |last11=Steiner |first11=Cynthia C. |last12=Chemnick |first12=Leona G. |display-authors=6 |date=2021-12-17 |editor-last=Murphy |editor-first=William J. |title=Facultative Parthenogenesis in California Condors |journal=[Journal of Heredity](/source/Journal_of_Heredity) |volume=112 |issue=7 |pages=569–574 |doi=10.1093/jhered/esab052 |pmc=8683835 |pmid=34718632 |url=https://academic.oup.com/jhered/article/112/7/569/6412509}}</ref> In times of stress, offspring produced by sexual reproduction may be fitter as they have new, possibly beneficial gene combinations. In addition, sexual reproduction provides the benefit of meiotic recombination between non-[sister chromosomes](/source/Sister_chromatids), a process associated with repair of [DNA](/source/DNA) double-strand breaks and other DNA damages that may be induced by stressful conditions.<ref>{{Cite book |last1=Bernstein |first1=H. |last2=Hopf |first2=F.A. |last3=Michod |first3=R.E. |chapter=The Molecular Basis of the Evolution of Sex |year=1987 |title=Molecular Genetics of Development |series=Advances in Genetics |volume=24 |pages=323–370 |doi=10.1016/s0065-2660(08)60012-7 |pmid=3324702 |isbn=978-0-12-017624-3}}</ref>

Many taxa with heterogony have within them species that have lost the sexual phase and are now completely asexual. Many other cases of obligate parthenogenesis (or gynogenesis) are found among polyploids and hybrids where the chromosomes cannot pair for meiosis.<ref>{{Cite journal |last=Dufresne |first=France |title=Parthenogenesis |url=https://academic.oup.com/book/41106/chapter/350407871 |access-date=2024-11-28 |website=academic.oup.com |date=2020 |pages=242–274 |doi=10.1093/oso/9780190688554.003.0009|isbn=978-0-19-068855-4 |url-access=subscription }}</ref>

The production of female offspring by parthenogenesis is referred to as [thelytoky](/source/thelytoky) (e.g., aphids) while the production of males by parthenogenesis is referred to as [arrhenotoky](/source/arrhenotoky) (e.g., bees). When unfertilized eggs develop into both males and females, the phenomenon is called deuterotoky.<ref name="Gavrilov-2007">{{cite journal |last1=Gavrilov |first1=I.A. |last2=Kuznetsova |first2=V.G. |title=On some terms used in the cytogenetics and reproductive biology of scale insects (Homoptera: Coccinea) |journal=Comparative Cytogenetics |year=2007 |volume=1 |issue=2 |pages=169–174 |url=http://www.zin.ru/Journals/compcyt/pdf/1/GavrilovKuznetsova.pdf}}</ref>

== Types and mechanisms ==

Parthenogenesis can occur without meiosis through mitotic oogenesis. This is called ''apomictic parthenogenesis''. Mature egg cells are produced by mitotic divisions, and these cells directly develop into embryos. In flowering plants, cells of the [gametophyte](/source/gametophyte) can undergo this process. The offspring produced by apomictic parthenogenesis are full clones of their mother, as in aphids.<ref>{{Cite journal |last=BLACKMAN |first=ROGER L. |date=1979-05-01 |title=Stability and variation in aphid clonal lineages |url=https://academic.oup.com/biolinnean/article-abstract/11/3/259/2682691?redirectedFrom=fulltext |journal=Biological Journal of the Linnean Society |volume=11 |issue=3 |pages=259–277 |doi=10.1111/j.1095-8312.1979.tb00038.x |bibcode=1979BJLS...11..259B |issn=0024-4066|url-access=subscription }}</ref>

Parthenogenesis involving [meiosis](/source/meiosis) is more complicated. In some cases, the offspring are haploid (e.g., male [ants](/source/ants)). In other cases, collectively called ''automictic parthenogenesis'', the ploidy is restored to diploidy by various means. This is because haploid individuals are not viable in most species. In automictic parthenogenesis, the offspring differ from one another and their mother. They are called ''half clones'' of their mother.<ref>{{Cite journal |last1=Booth |first1=Warren |last2=Smith |first2=Charles F. |last3=Eskridge |first3=Pamela H. |last4=Hoss |first4=Shannon K. |last5=Mendelson |first5=Joseph R. |last6=Schuett |first6=Gordon W. |date=2012-12-23 |title=Facultative parthenogenesis discovered in wild vertebrates |journal=Biology Letters |language=en |volume=8 |issue=6 |pages=983–985 |doi=10.1098/rsbl.2012.0666 |issn=1744-9561 |pmc=3497136 |pmid=22977071 |bibcode=2012BiLet...8..983B }}</ref>

=== Automixis ===
<!--this section is totally chaotic, badly written, ridiculously technical, sketchy, and poorly cited all at once: needs total rewrite-->
[[File:Central fusion and terminal fusion automixis.svg|thumb|280px|right|The effects of central fusion and terminal fusion on [heterozygosity](/source/heterozygosity) ]]

Automixis includes several reproductive mechanisms, some of which are parthenogenetic.<ref name="Engelstädter-2017">{{Cite journal |title=Asexual but Not Clonal: Evolutionary Processes in Automictic Populations &#124; Genetics |journal=Genetics |volume=206 |issue=2 |pages=993–1009 |doi=10.1534/genetics.116.196873 |pmid=28381586 |pmc=5499200 |year=2017 |last1=Engelstädter |first1=Jan}}</ref><ref name="Mogie-1986">{{cite journal |last1=Mogie |first1=Michael |title=Automixis: its distribution and status |journal=Biological Journal of the Linnean Society |volume=28 |pages=321–329 |year=1986 |doi=10.1111/j.1095-8312.1986.tb01761.x |issue=3}}</ref>

Diploidy can be restored by the doubling of the chromosomes without cell division before meiosis begins or after meiosis is completed. This is an [endomitotic](/source/Endoreduplication) cycle. Diploidy can also be restored by fusion of the first two [blastomeres](/source/blastomeres), or by fusion of the meiotic products. The chromosomes may not separate at one of the two anaphases (restitutional meiosis)l or the nuclei produced may fuse, or one of the polar bodies may fuse with the egg cell at some stage during its maturation.{{cn|date=July 2024}}

Some authors consider all forms of automixis sexual as they involve recombination. Many others classify the endomitotic variants as asexual and consider the resulting embryos parthenogenetic. Among these authors, the threshold for classifying automixis as a sexual process depends on when the products of anaphase I or of anaphase II are joined. The criterion for sexuality varies from all cases of restitutional meiosis,<ref name="Zakharov-2005">{{cite journal |doi=10.1007/s11177-005-0103-z |volume=41 |issue=4 |pages=402–411 |last=Zakharov |first=I. A. |title=Intratetrad mating and its genetic and evolutionary consequences |journal=Russian Journal of Genetics |date=April 2005 |pmid=15909911 |s2cid=21542999}}</ref> to those where the nuclei fuse or to only those where gametes are mature at the time of fusion.<ref name="Mogie-1986" /> 

The genetic composition of the offspring depends on what type of automixis takes place. When endomitosis occurs before meiosis<ref name="Cosín-2011">Cosín, Darío J. Díaz, Marta Novo, and Rosa Fernández. "Reproduction of Earthworms: Sexual Selection and Parthenogenesis". In ''Biology of Earthworms'', edited by Ayten Karaca, 24:69–86. Berlin, Heidelberg: Springer Berlin Heidelberg, 2011. https://doi.org/10.1007%2F978-3-642-14636-7_5.</ref><ref name="Cuellar-1971">{{cite journal |doi=10.1002/jmor.1051330203 |volume=133 |issue=2 |pages=139–165 |last=Cuellar |first=Orlando |title=Reproduction and the mechanism of meiotic restitution in the parthenogenetic lizard Cnemidophorus uniparens |journal=Journal of Morphology |date=1971-02-01 |pmid=5542237 |bibcode=1971JMorp.133..139C |s2cid=19729047}}</ref> or when ''central fusion'' occurs (restitutional meiosis of anaphase I or the fusion of its products), the offspring get all<ref name="Cosín-2011" /><ref name="Lokki-1975">{{cite journal |volume=79 |issue=3 |pages=513–525 |last=Lokki |first=Juhani |author2=Esko Suomalainen |author3=Anssi Saura |author4=Pekka Lankinen |title=Genetic Polymorphism and Evolution in Parthenogenetic Animals. Ii. Diploid and Polyploid Solenobia Triquetrella (lepidoptera: Psychidae) |journal=Genetics |access-date=2011-12-20 |date=1975-03-01 |doi=10.1093/genetics/79.3.513 |url=http://www.genetics.org/content/79/3/513.abstract |pmid=1126629 |pmc=1213290}}</ref> to more than half of the mother's genetic material and heterozygosity is mostly preserved<ref name="Groot-2003">{{cite journal |volume=90 |issue=2 |pages=130–135 |last=Groot |first=T. V. M. |author2=E Bruins |author3=J. A. J. Breeuwer |title=Molecular genetic evidence for parthenogenesis in the Burmese python, ''Python molars bivittatus'' |journal=Heredity |date=2003-02-28 |doi=10.1038/sj.hdy.6800210 |pmid=12634818 |bibcode=2003Hered..90..130G |citeseerx=10.1.1.578.4368 |s2cid=2972822}}</ref> (if the mother has two alleles for a locus, the offspring will likely get both). This is because in [anaphase I](/source/anaphase_I) the homologous chromosomes are separated. Heterozygosity is not completely preserved when crossing over occurs in central fusion.<ref name="Pearcy-2004">{{cite journal |last1=Pearcy |first1=M. |last2=Aron |first2=S |last3=Doums |first3=C. |last4=Keller |first4=L |title=Conditional Use of Sex and Parthenogenesis for Worker and Queen Production in Ants |journal=Science |volume=306 |issue=5702 |pages=1780–1783 |year=2004 |pmid=15576621 |doi=10.1126/science.1105453 |bibcode=2004Sci...306.1780P |s2cid=37558595 |url=https://serval.unil.ch/notice/serval:BIB_B02C2CCCBCB4|hdl=2013/ULB-DIPOT:oai:dipot.ulb.ac.be:2013/18807 |hdl-access=free }}</ref> In the case of pre-meiotic doubling, recombination, if it happens, occurs between identical sister chromatids.<ref name="Cosín-2011" />

If ''terminal fusion'' (restitutional meiosis of anaphase II or the fusion of its products) occurs, a little over half of the mother's genetic material is present in the offspring, and the offspring are mostly homozygous.<ref name="Booth-2011">{{cite journal |doi=10.1093/jhered/esr080 |volume=102 |issue=6 |pages=759–763 |last=Booth |first=Warren|author2=Larry Million |author3=R. Graham Reynolds |author4=Gordon M. Burghardt |author5=Edward L. Vargo |author6-link=Coby Schal |author6=Coby Schal |author7=Athanasia C. Tzika |author8=Gordon W. Schuett |title=Consecutive Virgin Births in the New World Boid Snake, the Colombian Rainbow Boa, ''Epicrates maurus'' |journal=Journal of Heredity |date=December 2011 |pmid=21868391 |doi-access=free|citeseerx=10.1.1.414.384 }}</ref> This is because at anaphase II the [sister chromatids](/source/sister_chromatids) are separated and whatever heterozygosity is present is due to crossing over. In the case of endomitosis after meiosis, the offspring is completely homozygous and has only half the mother's genetic material.{{cn|date=October 2024}} This can result in parthenogenetic offspring being unique from each other and from their mother. {{cn|date=July 2024}}

=== Sex of the offspring ===

In apomictic parthenogenesis, the offspring are clones of the mother and hence (except for aphids) are usually female. In the case of aphids, parthenogenetically produced males and females are clones of their mother except that the males lack one of the X chromosomes (XO).<ref name="Hales-2002">{{cite journal |last1=Hales |first1=Dinah F. |last2=Wilson |first2=Alex C. C. |last3=Sloane |first3=Mathew A. |last4=Simon |first4=Jean-Christophe |last5=Legallic |first5=Jean-François |last6=Sunnucks |first6=Paul |year=2002 |title=Lack of detectable genetic recombination on the X&nbsp;chromosome during the parthenogenetic production of female and male aphids |journal=[Genetics Research](/source/Genetics_Research) |volume=79 |issue=3 |pages=203–209 |pmid=12220127 |doi=10.1017/S0016672302005657 |doi-access=free}}</ref>

When meiosis is involved, the sex of the offspring depends on the type of [sex determination system](/source/sex_determination_system) and the type of apomixis. In species that use the [XY sex-determination system](/source/XY_sex-determination_system), parthenogenetic offspring have two X chromosomes and are female. In species that use the [ZW sex-determination system](/source/ZW_sex-determination_system) the offspring genotype may be one of ZW (female),<ref name="Lokki-1975"/><ref name="Groot-2003"/> ZZ (male), or WW (non-viable in most species,<ref name="Booth-2011"/> but a fertile,{{dubious|can't check, source is embargoed, but abstract says the mother may be WO, not WW, and doesn't indicate that the WW offspring were fertile|date=December 2011}} viable female in a few, e.g., [boas](/source/Boidae)).<ref name="Booth-2011"/> ZW offspring are produced by [endoreplication](/source/endoreplication) before meiosis or by central fusion.<ref name="Lokki-1975"/><ref name="Groot-2003"/> ZZ and WW offspring occur either by terminal fusion<ref name="Booth-2011"/> or by endomitosis in the egg cell.{{cn|date=October 2024}}

In polyploid obligate parthenogens, like the whiptail lizard, all the offspring are female.<ref name="Cuellar-1971"/>

In many hymenopteran insects, such as honeybees, female eggs are produced sexually, using sperm from a drone father, while the production of further drones (males) depends on the queen (and occasionally workers) producing unfertilized eggs. This means that females (workers and queens) are always diploid, while males (drones) are always haploid and are produced parthenogenetically.{{cn|date=October 2024}}

=== Facultative ===

Facultative parthenogenesis occurs when a female can produce offspring either sexually or via asexual reproduction.<ref name="Bell-1982">Bell, G. (1982). ''The Masterpiece of Nature: The Evolution and Genetics of Sexuality'', University of California Press, Berkeley, pp. 1–635 (see p. 295). {{ISBN|978-0-520-04583-5}}</ref> Facultative parthenogenesis is extremely rare in nature, with only a few examples of animal taxa capable of facultative parthenogenesis.<ref name="Bell-1982" /> One of the best-known examples of taxa exhibiting facultative parthenogenesis are [mayflies](/source/mayflies); presumably, this is the default reproductive mode of all species in this insect order.<ref>{{cite journal|doi=10.1899/10-015.1|title=Why stream mayflies can reproduce without males but remain bisexual: A case of lost genetic variation|journal=Journal of the North American Benthological Society|volume=29|issue=4|pages=1258–1266|year=2010|last1=Funk|first1=David H.|last2=Sweeney|first2=Bernard W.|last3=Jackson|first3=John K.|s2cid=86088826}}</ref> Facultative parthenogenesis has generally been believed to be a response to a lack of a viable male. A female may undergo facultative parthenogenesis if a male is absent from the habitat or if it is unable to produce viable offspring. However, [California condor](/source/California_condor)s and the tropical lizard ''[Lepidophyma smithii](/source/Lepidophyma_smithii)'' both can produce parthenogenic offspring in the presence of males, indicating that facultative parthenogenesis may be more common than previously thought and is not simply a response to a lack of males.<ref name="Kratochvíl-2020"/><ref name="Ryder-2021">{{cite journal |last1=Ryder |first1=Oliver A. |last2=Thomas |first2=Steven |last3=Judson |first3=Jessica Martin |last4=Romanov |first4=Michael N. |last5=Dandekar |first5=Sugandha |last6=Papp |first6=Jeanette C. |last7=Sidak-Loftis |first7=Lindsay C. |last8=Walker |first8=Kelli |last9=Stalis |first9=Ilse H. |last10=Mace |first10=Michael |last11=Steiner |first11=Cynthia C. |last12=Chemnick |first12=Leona G. |display-authors=6 |date=2021-12-17 |title=Facultative parthenogenesis in California condors |journal=[Journal of Heredity](/source/Journal_of_Heredity) |volume=112 |issue=7 |pages=569–574 |doi=10.1093/jhered/esab052 |pmc=8683835 |pmid=34718632}}</ref>

In [aphids](/source/aphids), a generation sexually conceived by a male and a female produces only females. The reason for this is the [non-random segregation](/source/Non-random_segregation_of_chromosomes) of the [sex chromosomes](/source/sex_chromosomes) 'X' and 'O' during [spermatogenesis](/source/spermatogenesis).<ref>{{cite journal
 |last=Schwartz |first=Hermann |year=1932 |title=Der Chromosomenzyklus von Tetraneura ulmi de Geer |journal=Zeitschrift für Zellforschung und Mikroskopische Anatomie |volume=15 |issue=4 |pages=645–687 |s2cid=43030757 |doi=10.1007/BF00585855 |url=https://link.springer.com/article/10.1007/BF00585855|url-access=subscription }}</ref>

Facultative parthenogenesis is often used to describe cases of spontaneous parthenogenesis in normally sexual animals.<ref name="vanderKooi-2015">{{cite journal |last1=van der Kooi |first1=C.J. |last2=Schwander |first2=T. |year=2015 |title=Parthenogenesis: Birth of a new lineage or reproductive accident? |journal=[Current Biology](/source/Current_Biology) |volume=25 |issue=15 |pages=R659–R661 |doi=10.1016/j.cub.2015.06.055 |doi-access=free |url=https://www.researchgate.net/publication/280691646 |pmid=26241141 |bibcode=2015CBio...25.R659V }}</ref> For example, many cases of spontaneous parthenogenesis in [sharks](/source/sharks), some [snakes](/source/snakes), [Komodo dragon](/source/Komodo_dragon)s, and a variety of domesticated birds were widely attributed to facultative parthenogenesis.<ref>{{cite journal |last=Lampert |first=K.P. |year=2008 |title=Facultative parthenogenesis in vertebrates: Reproductive error or chance? |journal=[Sexual Development](/source/Sexual_Development_(journal)) |volume=2 |issue=6 |pages=290–301 |doi=10.1159/000195678 |pmid=19276631 |s2cid=9137566}}</ref> These cases are examples of spontaneous parthenogenesis.<ref name="Bell-1982"/><ref name="vanderKooi-2015"/> The occurrence of such asexually produced eggs in sexual animals can be explained by a meiotic error, leading to eggs produced via [automixis](/source/automixis).<ref name="vanderKooi-2015"/><ref>{{cite book |last1=Suomalainen |first1=E. |display-authors=etal |year=1987 |title=Cytology and Evolution in Parthenogenesis |place=Boca Raton, Florida |publisher=CRC Press}}</ref>

=== Obligate ===

Obligate parthenogenesis is the process in which organisms exclusively reproduce through asexual means.<ref name="Stelzer-2010">{{cite journal |last1=Stelzer |first1=C.-P. |last2=Schmidt |first2=J. |last3=Wiedlroither |first3=A. |last4=Riss |first4=S. |year=2010 |title=Loss of sexual reproduction and dwarfing in a small metazoan |journal=[PLOS](/source/PLOS) |volume=5 |issue=9 |article-number=e12854 |doi=10.1371/journal.pone.0012854 |doi-access=free |pmid=20862222 |pmc=2942836 |bibcode=2010PLoSO...512854S }}</ref> Many species have transitioned to obligate parthenogenesis over evolutionary time. Well-documented transitions to obligate parthenogenesis have been found in numerous metazoan taxa, albeit through highly diverse mechanisms. These transitions often occur as a result of inbreeding or mutation within large populations.<ref name="Scheuerl-2011">{{cite journal |last1=Scheuerl |first1=Thomas |display-authors=etal |year=2011 |title=Phenotypic of an allele causing obligate parthenogenesis |journal=[Journal of Heredity](/source/Journal_of_Heredity) |volume=102 |issue=4 |pages=409–415|doi=10.1093/jhered/esr036 |pmid=21576287 |pmc=3113615 }} web. {{nobr|23 October 2012}}</ref> Some documented species, specifically salamanders and geckos, rely on obligate parthenogenesis as their major method of reproduction. As such, there are over 80 species of unisex reptiles (mostly lizards but including a single snake species, ''[Indotyphlops braminus](/source/Indotyphlops_braminus)''), amphibians, and fishes in nature for which males are no longer a part of the reproductive process.<ref name="Booth-2012">{{cite journal |last1=Booth |first1=W. |last2=Smith |first2=C.F. |last3=Eskridge |first3=P.H. |last4=Hoss |first4=S.K. |last5=Mendelson |first5=J.R. |last6=Schuett |first6=G.W. |year=2012 |title=Facultative parthenogenesis discovered in wild vertebrates |journal=Biology Letters |volume=8 |issue=6 |pages=983–985 |doi=10.1098/rsbl.2012.0666 |pmid=22977071 |pmc=3497136 |bibcode=2012BiLet...8..983B }}</ref> A female produces an ovum with a full set (two sets of genes) provided solely by the mother. Thus, a male is not needed to provide sperm to fertilize the egg. This form of asexual reproduction is thought in some cases to be a serious threat to biodiversity due to the subsequent lack of gene variation and potentially decreased fitness of the offspring.<ref name="Stelzer-2010"/>

Some invertebrate species that feature (partial) sexual reproduction in their native range are found to reproduce solely by parthenogenesis in areas to which they have been [introduced](/source/invasive_species).<ref name="Vorburger-2003a">{{cite journal |last1=Vorburger |first1=Christoph |year=2003 |title=Environmentally related patterns of reproductive modes in the aphid ''Myzus persicae'' and the predominance of two 'superclones' in Victoria, Australia |journal=[Molecular Ecology](/source/Molecular_Ecology_(journal)) |volume=12 |issue=12 |pages=3493–3504 |doi=10.1046/j.1365-294X.2003.01998.x |pmid=14629364 |bibcode=2003MolEc..12.3493V |s2cid=32192796}}</ref><ref name="Caron-2013">{{cite journal |author1=Caron, V. |author2=Norgate, M. |author3=Ede, F.J. |author4=Nyman, T. |year=2013 |title=Novel microsatellite DNA markers indicate strict parthenogenesis and few genotypes in the invasive willow sawfly ''Nematus oligospilus'' |journal=[Bulletin of Entomological Research](/source/Bulletin_of_Entomological_Research) |volume=103 |issue=1 |pages=74–88 |doi=10.1017/S0007485312000429 |pmid=22929915 |s2cid=25210471 |url=https://www.zora.uzh.ch/id/eprint/75009/1/Bulletin_of_Entomological_Research_2013_74-88.pdf}}</ref> Relying solely on parthenogenetic reproduction has several advantages for an [invasive species](/source/invasive_species): it obviates the need for individuals in a very sparse initial population to search for mates; and an exclusively female sex distribution allows a population to multiply and invade more rapidly (potentially twice as fast). Examples include several [aphid](/source/aphid) species<ref name="Vorburger-2003a"/> and the willow sawfly, ''[Nematus oligospilus](/source/Nematus_oligospilus)'', which is sexual in its native [Holarctic](/source/Holarctic_realm) habitat but parthenogenetic where it has been introduced into the Southern Hemisphere.<ref name="Caron-2013"/>

== Natural occurrence ==

{{further|List of taxa that use parthenogenesis}}

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Parthenogenesis does not apply to [isogamous](/source/Isogamy) species.<ref>{{Cite book |last=Smith |first=John Maynard |author-link=John Maynard Smith |url=https://books.google.com/books?id=SbI5AAAAIAAJ&q=isogamous+species&pg=PA39 |title=The Evolution of Sex |publisher=CUP Archive |year=1978 |isbn=978-0-521-21887-0 |page=42}}</ref> Parthenogenesis occurs naturally in [aphid](/source/aphid)s, ''[Daphnia](/source/Daphnia)'', [rotifer](/source/rotifer)s, [nematode](/source/nematode)s, and some other invertebrates, as well as in many plants. Among [vertebrates](/source/vertebrates), strict parthenogenesis is only known to occur in lizards, snakes,<ref name="Price-1992">{{cite journal |last=Price |first=A.H. |year=1992 |title=Comparative behavior in lizards of the genus ''Cnemidophorus'' (Teiidae), with comments on the evolution of parthenogenesis in reptiles |journal=[Copeia](/source/Ichthyology_%26_Herpetology) |volume=1992 |issue=2 |pages=323–331|doi=10.2307/1446193 |jstor=1446193 }}</ref> birds,<ref name="Schut-2008">{{cite journal |last1=Schut |first1=E. |last2=Hemmings |first2=N. |last3=Birkhead |first3=T.R. |year=2008 |title=Parthenogenesis in a passerine bird, the Zebra finch ''Taeniopygia guttata'' |journal=[Ibis](/source/Ibis_(journal)) |volume=150 |issue=1 |pages=197–199 |doi=10.1111/j.1474-919x.2007.00755.x}}</ref> and sharks.<ref name="Chapman-2007">{{cite journal |last1=Chapman |first1=Demian D. |author2=Shivji, Mahmood S. |author3=Louis, Ed |author4=Sommer, Julie |author5=Fletcher, Hugh |author6=Prodöhl, Paulo A. |title=Virgin birth in a hammerhead shark |journal=[Biology Letters](/source/Biology_Letters) |year=2007 |volume=3 |issue=4 |pages=425–427 |doi=10.1098/rsbl.2007.0189 |pmid=17519185 |pmc=2390672 |bibcode=2007BiLet...3..425C }}</ref> Fish, amphibians, and reptiles make use of various forms of gynogenesis and hybridogenesis (an incomplete form of parthenogenesis).<ref name="Vrijenhoek-1989"/> The first all-female (unisexual) reproduction in [vertebrates](/source/vertebrates) was described in the fish ''[Poecilia formosa](/source/Poecilia_formosa)'' in 1932.<ref name="Hubbs-1932">{{cite journal |last1=Hubbs |first1=C.L. |last2=Hubbs |first2=L.C. |year=1932 |title=Apparent parthenogenesis in nature, in a form of fish of hybrid origin |journal=[Science](/source/Science_(journal)) |volume=76 |issue=1983 |pages=628–630 |doi=10.1126/science.76.1983.628 |pmid=17730035 |bibcode=1932Sci....76..628H}}</ref> Since then, at least 50 species of unisexual vertebrates have been described, including at least 20 fish, 25 lizards, a single snake species, frogs, and salamanders.<ref name="Vrijenhoek-1989">Vrijenhoek, R.C., R.M. Dawley, C.J. Cole, and J.P. Bogart. 1989. "A list of the known unisexual vertebrates", pp. 19–23 ''in'': ''Evolution and Ecology of Unisexual Vertebrates''. R.M. Dawley and J.P. Bogart (eds.) Bulletin 466, New York State Museum, Albany</ref><!--

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== Artificial induction ==

Use of an electrical or chemical stimulus can produce the beginning of the process of parthenogenesis in the asexual development of viable offspring.<ref>{{cite journal |last1=Versieren |first1=K |last2=Heindryckx |first2=B |last3=Lierman |first3=S |last4=Gerris |first4=J |last5=De Sutter |first5=P. |year=2010 |title=Developmental competence of parthenogenetic mouse and human embryos after chemical or electrical activation |journal=Reprod Biomed |volume=21 |issue=6|pages= 769–775 |doi=10.1016/j.rbmo.2010.07.001 |pmid=21051286|doi-access=free}}</ref> thumb|upright=2|Induction of parthenogenesis in pigs<ref name="Bischoff-2009"/><ref name="Mori-2008">{{cite journal |last1=Mori |first1=Hironori |last2=Mizobe |first2=Yamato |last3=Inoue |first3=Shin |last4=Uenohara |first4=Akari |last5=Takeda |first5=Mitsuru |last6=Yoshida |first6=Mitsutoshi |last7=Miyoshi |first7=Kazuchika |title=Effects of Cycloheximide on Parthenogenetic Development of Pig Oocytes Activated by Ultrasound Treatment |journal=Journal of Reproduction and Development |volume=54 |issue=5 |pages=364–369 |year=2008 |pmid=18635923 |doi=10.1262/jrd.20064|doi-access=free}}</ref>

During oocyte development, high metaphase-promoting factor (MPF) activity causes mammalian oocytes to arrest at the metaphase II stage until fertilization by a sperm. The fertilization event causes intracellular calcium oscillations and targeted degradation of cyclin B, a regulatory subunit of MPF, thus permitting the MII-arrested oocyte to proceed through meiosis.<ref name="Bischoff-2009"/><ref name="Mori-2008"/>

To initiate unfertilised development of swine oocytes, various methods exist to induce an artificial activation that mimics sperm entry, such as calcium ionophore treatment, microinjection of calcium ions, or electrical stimulation. Treatment with cycloheximide, a non-specific protein synthesis inhibitor, enhances the development of unfertilised eggs in swine presumably by continual inhibition of MPF/cyclin B.<ref name="Mori-2008" /> As meiosis proceeds, extrusion of the second polar is blocked by exposure to cytochalasin B. This treatment results in a diploid (2 maternal genomes) parthenote<ref name="Bischoff-2009" /> The resulting embryos can be surgically transferred to a recipient oviduct for further development, but will succumb to developmental failure after ≈30 days of gestation. The swine placenta in these cases often appears hypo-vascular: see free image (Figure 1) in linked reference.<ref name="Bischoff-2009"/>

Induced parthenogenesis of this type in [mice](/source/mouse) and [monkey](/source/monkey)s results in abnormal development. This is because mammals have [imprinted](/source/Genomic_imprinting) genetic regions, where either the maternal or the paternal chromosome is inactivated in the offspring for development to proceed normally. A mammal developing from parthenogenesis would have double doses of maternally imprinted genes and lack paternally imprinted genes, leading to developmental abnormalities. It has been suggested that defects in [placenta](/source/placenta)l folding or interdigitation are one cause of swine parthenote abortive development.<ref name="Bischoff-2009">{{cite journal |last1=Bischoff |first1=S.R. |last2=Tsai |first2=S. |last3=Hardison |first3=N. |last4=Motsinger-Reif |first4=A.A. |last5=Freking |first5=B.A. |last6=Nonneman |first6=D. |last7=Rohrer |first7=G. |last8=Piedrahita |first8=J.A. |display-authors=6 |title=Characterization of conserved and nonconserved imprinted genes in swine |journal=[Biology of Reproduction](/source/Biology_of_Reproduction) |volume=81 |issue=5 |pages=906–920 |year=2009 |pmid=19571260 |pmc=2770020 |doi=10.1095/biolreprod.109.078139}}</ref> As a consequence, research on the induced development of unfertilised eggs in humans is focused on the production of [embryonic stem cells](/source/embryonic_stem_cells) for use in medical treatment, not as a reproductive strategy.

In 2022, researchers reported that they had produced viable offspring born from unfertilized eggs in mice, addressing the problems of genomic imprinting by "targeted DNA methylation rewriting of seven imprinting control regions".<ref name="Wei-2022" />

== In humans ==
In 1955, [Helen Spurway](/source/Helen_Spurway), a geneticist specializing in the reproductive biology of the [guppy](/source/guppy) (''Poecilia reticulata''), claimed that parthenogenesis may occur (though very rarely) in humans, leading to so-called "virgin births". This created some sensation among her colleagues and the lay public alike.<ref>''Time'', 28 November 1955; Editorial in ''The Lancet'', 2: 967 (1955)</ref> Sometimes an embryo may begin to divide without fertilization, but it cannot fully develop on its own; so while it may create some skin and nerve cells, it cannot create others (such as skeletal muscle) and becomes a type of benign tumor called an ovarian [teratoma](/source/teratoma).<ref name="de Carli-2017">{{Cite journal |last1=Jose de Carli |first1=Gabriel |last2=Campos Pereira |first2=Tiago |date=September 2017 |title=On human parthenogenesis |journal=Medical Hypotheses |language=en |volume=106 |pages=57–60 |doi=10.1016/j.mehy.2017.07.008|pmid=28818272 |doi-access=free }}</ref> Spontaneous ovarian activation is not rare and has been known about since the 19th century. Some teratomas can even become primitive fetuses (fetiform teratoma) with imperfect heads, limbs, and other structures, but are non-viable.{{cn|date=October 2024}}

In 1995, there was a reported case of partial human parthenogenesis; a boy was found to have some of his cells (such as [white blood cell](/source/white_blood_cell)s) lacking any genetic content from his father. Scientists believe that an unfertilized egg began to self-divide but then had some (but not all) of its cells fertilized by a sperm cell; this must have happened early in development, as self-activated eggs quickly lose their ability to be fertilized. The unfertilized cells eventually duplicated their DNA, boosting their chromosomes to 46. When the unfertilized cells hit a developmental block, the fertilized cells took over and developed that tissue. The boy had asymmetrical facial features and learning difficulties, but was otherwise healthy. This would make him a parthenogenetic [chimera](/source/Chimera_(genetics)) (a child with two cell lineages in his body).<ref>Philip Cohen, [https://www.newscientist.com/article/mg14819982-300-the-boy-whose-blood-has-no-father/ "The boy whose blood has no father"], ''New Scientist'', 7.10.1995</ref> While over a dozen similar cases have been reported since then (usually discovered after the patient demonstrated clinical abnormalities), there have been no scientifically confirmed reports of a non-chimeric, clinically healthy human parthenote, i.e., produced from a single, parthenogenetic-activated oocyte.<ref name="de Carli-2017" />

In 2007, the International Stem Cell Corporation of California announced that Elena Revazova had intentionally created human stem cells from unfertilized human eggs using parthenogenesis. The process may offer a way to create stem cells genetically matched to a particular female to treat degenerative diseases. The same year, Revazova and ISCC published an article describing how to produce human stem cells that are [homozygous](/source/Homozygous) in the [HLA](/source/human_leukocyte_antigen) region of DNA.<ref>{{cite journal |last1=Revazova |first1=E.S. |last2=Turovets |first2=N.A. |last3=Kochetkova |first3=O.D. |last4=Kindarova |first4=L.B. |last5=Kuzmichev |first5=L.N. |last6=Janus |first6=J.D. |last7=Pryzhkova |first7=M.V. |title=Patient-Specific Stem Cell Lines Derived from Human Parthenogenetic Blastocysts |journal=Cloning and Stem Cells |volume=9 |issue=3 |pages=432–449 |year=2007 |pmid=17594198 |doi=10.1089/clo.2007.0033}}</ref> These stem cells are called HLA homozygous parthenogenetic human stem cells (hpSC-Hhom) and would allow derivatives of these cells to be implanted without immune rejection. With the selection of oocyte donors according to HLA [haplotype](/source/haplotype), it would be possible to generate a bank of cell lines whose tissue derivatives, collectively, could be [MHC-matched](/source/Major_histocompatibility_complex) with a significant number of individuals within the human population.<ref name="Revazova-2008">{{cite journal |last1=Revazova |first1=E.S. |last2=Turovets |first2=N.A. |last3=Kochetkova |first3=O.D. |last4=Agapova |first4=L.S. |last5=Sebastian |first5=J.L. |last6=Pryzhkova |first6=M.V. |last7=Smolnikova |first7=V.Iu. |last8=Kuzmichev |first8=L.N. |last9=Janus |first9=J.D. |display-authors=6 |title=HLA homozygous stem cell lines derived from human parthenogenetic blastocysts |journal=Cloning and Stem Cells |volume=10 |issue=1 |pages=11–24 |year=2008 |pmid=18092905 |doi=10.1089/clo.2007.0063}}</ref>

After an independent investigation, it was revealed that the discredited South Korean scientist [Hwang Woo-suk](/source/Hwang_Woo-suk) unknowingly produced the first human embryos resulting from parthenogenesis. Initially, Hwang claimed he and his team had extracted stem cells from cloned human embryos, a result later found to be fabricated. Further examination of the chromosomes of these cells shows indicators of parthenogenesis in those extracted stem cells, similar to those found in the [mice](/source/Kaguya_(mouse)) created by Tokyo scientists in 2004. Although Hwang deceived the world about being the first to create artificially cloned human embryos, he contributed a breakthrough to stem cell research by creating human embryos using parthenogenesis.<ref>Williams, Chris. [http://www.theregister.com/2007/08/03/hwang_parthenogenesis/ "Stem cell fraudster made 'virgin birth' breakthrough: Silver lining for Korean science scandal"], ''The Register'', 3 August 2007.</ref>

== Similar phenomena ==

=== Androgenesis ===
[Androgenesis](/source/Androgenesis) is a system of asexual reproduction and occurs when a zygote is produced with only paternal nuclear genes. Requiring the presence of eggs, one of two things can occur to produce offspring with exclusively paternal genetic material: The maternal nuclear genome can be eliminated from the zygote, or the female can produce an egg with no nucleus, resulting in an embryo developing with only the genome of the male gamete. Although androgenesis requires both male and females gametes, it is not strictly considered a form of sexual reproduction, because the offspring have uniparental nuclear DNA that has not undergone recombination, and the proliferation of androgenesis can lead to exclusively asexually reproducing species. One example of androgenesis is the iberian fish Calandino.

=== Gynogenesis ===
{{See also|Gynogenesis|Parthenogenesis in amphibians#Gynogenesis}}

A form of asexual reproduction related to parthenogenesis is gynogenesis. Here, offspring are produced by the same mechanism as in parthenogenesis, but with the requirement that the egg merely be stimulated by the ''presence'' of [sperm](/source/sperm) to develop. However, the sperm cell does not contribute any genetic material to the offspring. Since gynogenetic species are all female, activation of their eggs requires mating with males of a closely related species for the needed stimulus. Some [salamander](/source/salamander)s of the genus ''[Ambystoma](/source/Ambystoma)'' are gynogenetic and appear to have been so for over a million years. The success of those salamanders may be due to rare fertilization of eggs by males, introducing new material to the gene pool, which may result from perhaps only one mating out of a million. In addition, the [Amazon molly](/source/Amazon_molly) is known to reproduce by gynogenesis.<ref>{{cite news |title=No sex for all-girl fish species |url=https://news.bbc.co.uk/2/hi/uk_news/scotland/edinburgh_and_east/7360770.stm |access-date=2007-06-11 |website=[BBC News](/source/BBC_News) |date=23 April 2008}}</ref>

=== Hybridogenesis ===

{{See also|Hybridogenesis in water frogs}}

[[File:Hybridogenesis in water frogs.gif|thumb|center|500px|Example crosses between [pool frog](/source/pool_frog) (''Pelophylax lessonae''), [marsh frog](/source/marsh_frog) (''P. ridibundus'') and their hybrid – [edible frog](/source/edible_frog) (''P.'' kl. ''esculentus''). On the left, primary hybridisation generating a hybrid, while the middle is the most widespread type of hybridogenesis.<ref name="Holsbeek-2010" /><ref name="Vorburger-2003b" />]]

Hybridogenesis is a mode of reproduction of [hybrids](/source/Hybrid_(biology)). Hybridogenetic hybrids (for example AB [genome](/source/genome)), usually females, during [gametogenesis](/source/gametogenesis) exclude one of parental genomes (A) and produce [gamete](/source/gamete)s with [unrecombined](/source/Genetic_recombination)<ref name="Holsbeek-2010" /> [genome](/source/genome) of second parental species (B), instead of containing mixed recombined parental genomes. First genome (A) is restored by [fertilization](/source/fertilization) of these gametes with gametes from the first species (AA, sexual host,<ref name="Holsbeek-2010" /> usually male).<ref name="Holsbeek-2010" /><ref name="Schultz-1969" /><ref name="Vrijenhoek-1998"/> Hybridogenesis is not completely asexual, but hemiclonal: half the genome is passed to the next generation [clonally](/source/Clone_(cell_biology)), unrecombined, intact (B), other half [sexually](/source/Sexual_reproduction), recombined (A). This process continues, so that each generation is half (or hemi-) clonal on the mother's side and has half new genetic material from the father's side.<ref name="Holsbeek-2010"/><ref name="Simon-2003"/>

This form of reproduction is seen in some live-bearing fish of the genus ''[Poeciliopsis](/source/Poeciliopsis)''<ref name="Schultz-1969" /><ref name="Vrijenhoek-1992" /> as well as in some of the ''[Pelophylax](/source/Pelophylax)'' spp. ("green frogs" or "waterfrogs"):
* ''[P. kl. esculentus](/source/Pelophylax_kl._esculentus)'' (edible frog): ''[P. lessonae](/source/Pelophylax_lessonae)'' × ''[P. ridibundus](/source/Pelophylax_ridibundus)'',<ref name="Holsbeek-2010" /><ref name="tolweb-2014" /><ref name="Beukeboom-1998" />
* ''[P. kl. grafi](/source/Pelophylax_kl._grafi)'' (Graf's hybrid frog): ''[P. perezi](/source/Pelophylax_perezi)'' × ''[P. ridibundus](/source/Pelophylax_ridibundus)''<ref name="Holsbeek-2010" />
* ''[P. kl. hispanicus](/source/Pelophylax_kl._hispanicus)'' (Italian edible frog) – unknown origin: ''[P. bergeri](/source/Pelophylax_bergeri)'' × ''[P. ridibundus](/source/Pelophylax_ridibundus)'' or ''[P. kl. esculentus](/source/Pelophylax_kl._esculentus)''<ref name="Holsbeek-2010" />

Other examples where hybridogenesis is at least one of the modes of reproduction include i.e.,
* Iberian minnow ''[Tropidophoxinellus alburnoides](/source/Tropidophoxinellus_alburnoides)'' (''[Squalius pyrenaicus](/source/Squalius_pyrenaicus)'' × hypothetical ancestor related with ''[Anaecypris hispanica](/source/Anaecypris_hispanica)'')<ref name="Inácio-2012" />
* spined loaches ''[Cobitis](/source/Cobitis) hankugensis'' × ''C. longicorpus''<ref name="Saitoh-2004" />
* ''[Bacillus](/source/Bacillus_(insect))'' stick insects ''[B. rossius](/source/Bacillus_rossius)'' × ''Bacillus grandii benazzii''<ref name="Mantovani-1992" />

== In human culture ==
Parthenogenesis, in the form of reproduction from a mother alone, is common in mythology, religion, and folklore around the world, including in ancient [Greek myth](/source/Greek_mythology), in which [Gaia](/source/Gaia) (the earth) gives birth to [Ouranos](/source/Ouranos) (the heavens),<ref>Hesiod, ''Theogony'' [https://www.perseus.tufts.edu/hopper/text?doc=Hes.+Th.+126&fromdoc=Perseus%3Atext%3A1999.01.0130:chapter=126&highlight=Earth 126–128]</ref> and according to [Hesiod](/source/Hesiod) and others, the god [Hephaestus](/source/Hephaestus) is born from [Hera](/source/Hera).<ref>[Hesiod](/source/Hesiod), ''[Theogony](/source/Theogony)'' [https://www.perseus.tufts.edu/hopper/text?doc=Hes.+Th.+927&fromdoc=Perseus%3Atext%3A1999.01.0130 927–928]</ref> In Christianity and Islam, there is the [virgin birth of Jesus](/source/virgin_birth_of_Jesus), and stories of [miraculous births](/source/miraculous_births) also appear in other global religions.<ref>{{cite book |last1=Carrigan |first1=Henry L. |chapter=Virgin Birth |editor1-last=Freedman |editor1-first=David Noel |editor2-last=Myers |editor2-first=Allen C. |title=Eerdmans Dictionary of the Bible |publisher=Eerdmans |year=2000 |chapter-url=https://books.google.com/books?id=qRtUqxkB7wkC&pg=PA1359 |isbn=978-90-5356-503-2 |page=1359}}</ref>
The theme is one of several aspects of [reproductive biology explored in science fiction](/source/Reproduction_and_pregnancy_in_speculative_fiction).<ref name="Creed-1990">{{citation |last=Creed |first=Barbara |author-link=Barbara Creed |contribution=Gynesis, Postmodernism and Science Fiction Horror Film |editor-last=Kuhn |editor-first=Annette |editor-link=Annette Kuhn |title=Alien Zone: Cultural Theory and Contemporary Science Fiction Cinema |page=[https://archive.org/details/alienzonecultura0000unse/page/215 215] |publisher=Verso |location=London |year=1990 |isbn=978-0-86091-993-3 |url=https://archive.org/details/alienzonecultura0000unse/page/215 }}</ref>

== See also ==
* [Androgenesis](/source/Androgenesis) - a form of quasi-sexual reproduction in which a male is the sole source of the nuclear genetic material in the embryo
* [Telescoping generations](/source/Telescoping_generations)
* {{annotated link|Charles Bonnet}} – conducted experiments that established what is now termed parthenogenesis in aphids
* {{annotated link|Jan Dzierżon}} – Polish [apiarist](/source/apiarist) and a pioneer of parthenogenesis among [bees](/source/bees)
* {{annotated link|Jacques Loeb}} – caused the eggs of sea urchins to begin embryonic development without sperm
* {{annotated link|Parthenocarpy}} – plants with seedless fruit

==References==
{{Reflist|refs=

<ref name="Vrijenhoek-1992">{{cite journal |last1=Vrijenhoek |first1=J.M. |last2=Avise |first2=J.C. |last3=Vrijenhoek |first3=R.C. |date=1992-01-01 |title=An Ancient clonal lineage in the fish genus ''Poeciliopsis'' (Atheriniformes: Poeciliidae) |journal=Proceedings of the National Academy of Sciences USA |volume=89 |issue=1 |pages=348–352 |bibcode=1992PNAS...89..348Q |doi=10.1073/pnas.89.1.348 |doi-access=free |pmid=11607248 |pmc=48234 |issn=0027-8424}}</ref>

<ref name="tolweb-2014">{{cite web |title=Hybridogenesis in water frogs |website=tolweb.org |id=Note 579 |url=http://www.tolweb.org/notes/?note_id=579 |access-date=13 March 2007 |archive-date=14 July 2014 |archive-url=https://web.archive.org/web/20140714150953/http://www.tolweb.org/notes/?note_id=579 }}</ref>

<ref name="Beukeboom-1998">{{cite journal |last1=Beukeboom |first1=L.W. |last2=Vrijenhoek |first2=R.C. |year=1998 |title=Evolutionary genetics and ecology of sperm-dependent parthenogenesis |journal=[Journal of Evolutionary Biology](/source/Journal_of_Evolutionary_Biology) |volume=11 |issue=6 |pages=755–782 |s2cid=85833296 |doi=10.1046/j.1420-9101.1998.11060755.x |bibcode=1998JEBio..11..755B |doi-access=free}}</ref>

<ref name="Schultz-1969">{{cite journal |last=Schultz |first=R. Jack |date=November–December 1969 |title=Hybridization, unisexuality, and polyploidy in the teleost ''Poeciliopsis'' (Poeciliidae) and other vertebrates |journal=The American Naturalist |volume=103 |issue=934 |pages=605–619 |jstor=2459036 |doi=10.1086/282629|bibcode=1969ANat..103..605S |s2cid=84812427}}</ref>

<ref name="Holsbeek-2010">{{cite journal |last1=Holsbeek |first1=G. |last2=Jooris |first2=R. |date=2010 |title=Potential impact of genome exclusion by alien species in the hybridogenetic water frogs (''Pelophylax esculentus'' complex) |journal=Biological Invasions |volume=12 |issue=1 |pages=1–13 |doi=10.1007/s10530-009-9427-2 |bibcode=2010BiInv..12....1H |s2cid=23535815}}</ref>

<ref name="Vorburger-2003b">{{cite journal |last1=Vorburger |first1=Christoph |last2=Reyer |first2=Heinz-Ulrich |date=2003 |title=A genetic mechanism of species replacement in European waterfrogs? |journal=Conservation Genetics |volume=4 |issue=2 |pages=141–155 |url=http://www.zool.uzh.ch/static/research/oekologie/literatur/pdf05_01/Vorburger2003CG_4.pdf |doi=10.1023/A:1023346824722 |bibcode=2003ConG....4..141V |s2cid=20453910 |access-date=2015-06-21}}</ref>

<ref name="Inácio-2012">{{cite journal |last1=Inácio |first1=A |last2=Pinho |first2=J |last3=Pereira |first3=PM |last4=Comai |first4=L |last5=Coelho |first5=MM |year=2012 |title= Global Analysis of the Small RNA Transcriptome in Different Ploidies and Genomic Combinations of a Vertebrate Complex – The ''Squalius alburnoides'' |journal=PLOS ONE |volume=7 |issue=7: e41158 |pages=359–368 |doi=10.1371/journal.pone.0041158 |pmid=22815952 |pmc=3399795|bibcode=2012PLoSO...741158I|doi-access=free}}</ref>

<ref name="Saitoh-2004">{{cite journal |last1=Saitoh |first1=K |last2=Kim |first2=I-S |last3=Lee |first3=E-H |year=2004 |title= Mitochondrial gene introgression between spined loaches via hybridogenesis |journal=Zoological Science |volume=21 |issue=7 |pages=795–798 |doi=10.2108/zsj.21.795 |pmid=15277723 |s2cid=40846660|doi-access=free }}</ref>

<ref name="Mantovani-1992">{{cite journal |last1=Mantovani |first1=Barbara |last2=Scali |first2=Valerio |year=1992 |title= Hybridogenesis and androgenesis in the stick-insect ''Bacillus rossius''-''Grandii benazzii'' (Insecta, Phasmatodea) |journal=Evolution |volume=46 |issue=3 |pages=783–796 |doi=10.2307/2409646 |pmid=28568678 |jstor=2409646}}</ref>

<ref name="Vrijenhoek-1998">{{cite book |last=Vrijenhoek |first=Robert C. |editor-last=Knobil |editor-first=Ernst |editor2-last=Neill |editor2-first=Jimmy D. |date=1998 |chapter=Parthenogenesis and Natural Clones |title=Encyclopedia of Reproduction |volume=3 |publisher=Academic Press |isbn=978-0-12-227020-8 |pages=[https://archive.org/details/encyclopediaofre0000unse_f1r2/page/695 695–702] |chapter-url=http://www.mbari.org/staff/vrijen/PDFS/Vrijen_1999%20EncRep.pdf |url=https://archive.org/details/encyclopediaofre0000unse_f1r2/page/695}}</ref>

<ref name="Simon-2003">{{cite journal |last1=Simon |first1=J.-C. |last2=Delmotte |first2=F. |last3=Rispe |first3=C. |last4=Crease |first4=T. |year=2003 |title=Phylogenetic relationships between parthenogens and their sexual relatives: the possible routes to parthenogenesis in animals |journal=Biological Journal of the Linnean Society |volume=79 |pages= 151–163 |url=http://exa.unne.edu.ar/biologia/embriologia.animal/public_html/Bibliografia%20recomendada/Origen%20de%20la%20partenogenesis.pdf |access-date=2015-06-21|doi=10.1046/j.1095-8312.2003.00175.x|doi-access=free}}</ref>

}}

==Further reading==

{{Refbegin}}
* Dawley, Robert M. & Bogart, James P. (1989). ''Evolution and Ecology of Unisexual Vertebrates''. Albany: New York State Museum. {{ISBN|1-55557-179-4}}
* {{cite journal |last1=Fangerau |first1=H |title=Can artificial parthenogenesis sidestep ethical pitfalls in human therapeutic cloning? An historical perspective |journal=Journal of Medical Ethics |volume=31 |issue=12 |pages=733–735 |year=2005 |pmid=16319240 |pmc=1734065 |doi=10.1136/jme.2004.010199 |ref=none}}
* Futuyma, Douglas J. & Slatkin, Chicago. (1983). ''Coevolution''. Sunderland, Mass: Sinauer Associates. {{ISBN|0-87893-228-3 }}
* {{cite journal |last1=Hore |first1=T |last2=Rapkins |first2=R |last3=Graves |first3=J |title=Construction and evolution of imprinted loci in mammals |journal=Trends in Genetics |volume=23 |issue=9 |pages=440–448 |year=2007 |pmid=17683825 |doi=10.1016/j.tig.2007.07.003 |ref=none}}
* {{cite journal|author1=Kono, T. |author2=Obata, Y. |author3=Wu, Q. |author4=Niwa, K. |author5=Ono, Y. |author6=Yamamoto, Y. |author7=Park, E.S. |author8=Seo, J.-S. |author9=Ogawa, H. |year=2004 |title= Birth of parthenogenetic mice that can develop to adulthood |journal=Nature |volume=428 |issue=6985 |pages=860–864 |doi=10.1038/nature02402 |pmid=15103378|bibcode=2004Natur.428..860K |s2cid=4353479 |url=https://ir.ymlib.yonsei.ac.kr/handle/22282913/112977 |ref=none}}
* Maynard Smith, John. (1978). ''The Evolution of Sex''. Cambridge: [Cambridge University Press](/source/Cambridge_University_Press). {{ISBN|0-521-29302-2}}
* Michod, Richard E. & Levin, Bruce R. (1988). ''The Evolution of Sex''. Sunderland, Mass: Sinauer Associates. {{ISBN|0-87893-459-6}}
* {{cite journal |last1=Schlupp |first1=Ingo |title=The Evolutionary Ecology of Gynogenesis |journal=Annual Review of Ecology, Evolution, and Systematics |volume=36 |pages=399–417 |year=2005 |doi=10.1146/annurev.ecolsys.36.102003.152629 |ref=none}}
* {{cite journal |last1=Simon |first1=J |title=Ecology and evolution of sex in aphids |journal=Trends in Ecology & Evolution |volume=17 |pages=34–39 |year=2002 |doi=10.1016/S0169-5347(01)02331-X |last2=Rispe |first2=Claude |last3=Sunnucks |first3=Paul |ref=none}}
* Stearns, Stephan C. (1988). ''The Evolution of Sex and Its Consequences'' (Experientia Supplementum, Vol. 55). Boston: Birkhauser. {{ISBN|0-8176-1807-4}}
{{Refend}}

==External links==
* [http://www.utexas.edu/research/crewslab/index.html Reproductive behavior in whiptails at Crews Laboratory] {{Webarchive|url=https://web.archive.org/web/20100826023754/http://www.utexas.edu/research/crewslab/index.html |date=26 August 2010 }}
* [http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/A/AsexualReproduction.html Types of asexual reproduction]
* [http://oregonstate.edu/instruct/ans-tparth/ Parthenogenesis in Incubated Turkey Eggs] from Oregon State University
* [https://web.archive.org/web/20070103043255/http://news.nationalgeographic.com/news/2006/12/061220-virgin-dragons.html National Geographic News: Virgin Birth Expected at Christmas – By Komodo Dragon]
* [https://news.bbc.co.uk/2/hi/science/nature/6196225.stm "'Virgin births' for giant lizards (Komodo dragon)"] [BBC News](/source/BBC_News)
* [http://uk.reuters.com/article/idUKL243822920070125 Reuther: Komodo dragon proud mum (and dad) of five] {{Webarchive|url=https://web.archive.org/web/20210509034348/https://www.reuters.com/article/idUKL243822920070125?edition-redirect=uk |date=9 May 2021 }}
* [https://www.nbcnews.com/id/wbna18809674 Female sharks capable of virgin birth]
* [https://web.archive.org/web/20150214174512/http://www.nbcnews.com/id/27107721/ Scientists confirm shark's 'virgin birth' Article by Steve Szkotak AP updated 1:49 a.m. ET, Fri., 10 October 2008]
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Category:Asexual reproduction in animals
Category:Zoology

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Adapted from the Wikipedia article [Parthenogenesis](https://en.wikipedia.org/wiki/Parthenogenesis) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/Parthenogenesis?action=history)). Available under [Creative Commons Attribution-ShareAlike 4.0 International](https://creativecommons.org/licenses/by-sa/4.0/). Changes may have been made.