Parthenogenesis

File:Cnemidophorus-ThreeSpecies.jpg (center), which reproduces via parthenogenesis, is shown flanked by two sexual species having males, A. inornatus (left) and A. 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 |url=https://www.oxforddictionaries.com/definition/english/parthenogenesis |access-date=2016-01-20 |url-status=dead |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}}{{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., Medford & Somerville, MA }} q.v..) is a natural form of asexual reproduction in which the embryo develops directly from an egg without need for fertilization. In animals, parthenogenesis means the development of an embryo from an unfertilized egg cell. In plants, parthenogenesis is a component process of apomixis. In algae, parthenogenesis can mean the development of an embryo from either an individual sperm or an individual egg.

Parthenogenesis occurs naturally in some plants, algae, invertebrate animal species (including nematodes, some tardigrades, water fleas, some scorpions, aphids, some mites, some bees, some Phasmatodea, and parasitic wasps), and a few vertebrates, such as some fish, amphibians, and reptiles. This type of reproduction has been induced artificially in animal species that naturally reproduce through sex, including fish, amphibians, and mice.

Normal egg cells form in the process of meiosis and are haploid, with half as many chromosomes as their mother's body cells. Haploid individuals, however, are usually non-viable, and parthenogenetic offspring usually have the diploid chromosome number. Depending on the mechanism involved in restoring the diploid number of chromosomes, parthenogenetic offspring may have anywhere between all and half of the mother's alleles. In some types of parthenogenesis, the offspring that have all of the mother's genetic material are called full clones 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 of DNA takes place during meiosis, creating variation.

Parthenogenetic offspring in species that use either the XY or the X0 sex-determination system have two X chromosomes and are female. In species that use the 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

File:Parthkomodo.jpg, Varanus komodoensis, produced through parthenogenesis. Komodo dragons can produce offspring both through sexual reproduction and parthenogenesis.]]

Parthenogenesis is a form of asexual reproduction in which the embryo develops directly from an egg without need for fertilization.{{cite journal |last1=Heesch |first1=Svenja |author1-link=Svenja Heesch |last2=Serrano-Serrano |first2=Martha |last3=Barrera-Redondo |first3=Josué |last4=Luthringer |first4=Rémy |last5=Peters |first5=Akira F. |last6=Destombe |first6=Christophe |last7=Cock |first7=J. Mark |last8=Valero |first8=Myriam |last9=Roze |first9=Denis |last10=Salamin |first10=Nicolas |last11=Coelho |first11=Susana M. |display-authors=6 |date=July 2021 |title=Evolution of life cycles and reproductive traits: Insights from the brown algae |journal=Journal of Evolutionary Biology |volume=34 |issue=7 |pages=992–1009 |doi=10.1111/jeb.13880 |doi-access=free |pmid=34096650 |s2cid=92334399}}{{cite news |last=Preston |first=Elizabeth |date=13 February 2024 |title=Self-love is important, but we mammals are stuck with sex |newspaper=The New York Times |quote=Some female birds, reptiles, and other animals can make a baby on their own. But for mammals like us, eggs and sperm need each other. |url=https://www.nytimes.com/2024/02/13/science/valentines-day-sexual-reproduction-parthenogenesis.html |access-date=16 February 2024 |url-status=live |archive-url=https://archive.today/20240213114627/https://www.nytimes.com/2024/02/13/science/valentines-day-sexual-reproduction-parthenogenesis.html |archivedate=13 February 2024}} It occurs naturally in some plants, algae, invertebrate animal species (including nematodes, some tardigrades, water fleas, some scorpions, aphids, some mites, some bees, some Phasmatodea, and parasitic wasps), and a few vertebrates, such as some fish, amphibians, reptiles,{{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}}{{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}}{{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 |pages=171901 |doi=10.1098/rsos.171901 |pmc=5830781 |pmid=29515892 |bibcode=2018RSOS....571901A}} and birds.{{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 |url=http://oregonstate.edu/instruct/ans-tparth/index.html |url-status=dead |archive-url=https://web.archive.org/web/20120716235633/http://oregonstate.edu/instruct/ans-tparth/index.html |archive-date=2012-07-16}}{{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}} This type of reproduction has been induced artificially in several animal species that naturally reproduce through sex, including fish, amphibians, and mice.{{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 |volume=7 |issue=2 |pages=253–256 |pmid=21047849 |pmc=3061174 |doi=10.1098/rsbl.2010.0793}}{{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 |pages=e2115248119 |doi=10.1073/pnas.2115248119 |doi-access=free |pmid=35254875 |pmc=8944925 |bibcode=2022PNAS..11915248W}}

Some species reproduce exclusively by parthenogenesis (such as the bdelloid rotifers), while others can switch between sexual reproduction and parthenogenesis. This is called facultative parthenogenesis (other terms are cyclical parthenogenesis, heterogamy{{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}}{{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}} or heterogony{{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 |year=1984}}{{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}}). The switch between sexuality and parthenogenesis in such species may be triggered by the season (aphid, some gall wasps), or by a lack of males or by conditions that favour rapid population growth (rotifers and cladocerans like 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.{{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 |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}} In California condors, facultative parthenogenesis can occur even when a male is present and available for a female to breed with.{{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 |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}} 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, a process associated with repair of DNA double-strand breaks and other DNA damages that may be induced by stressful conditions.{{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}}

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.{{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 }}

The production of female offspring by parthenogenesis is referred to as thelytoky (e.g., aphids) while the production of males by parthenogenesis is referred to as arrhenotoky (e.g., bees). When unfertilized eggs develop into both males and females, the phenomenon is called deuterotoky.{{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}}

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 can undergo this process. The offspring produced by apomictic parthenogenesis are full clones of their mother, as in aphids.{{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 |issn=0024-4066|url-access=subscription }}

Parthenogenesis involving meiosis is more complicated. In some cases, the offspring are haploid (e.g., male 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.{{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}}

= Automixis =

File:Central fusion and terminal fusion automixis.svg ]]

Automixis includes several reproductive mechanisms, some of which are parthenogenetic.{{Cite journal |title=Asexual but Not Clonal: Evolutionary Processes in Automictic Populations | 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}}{{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}}

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 cycle. Diploidy can also be restored by fusion of the first two 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,{{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}} to those where the nuclei fuse or to only those where gametes are mature at the time of fusion. Those cases of automixis that are classified as sexual reproduction are compared to self-fertilization in their mechanism and consequences.{{cn|date=July 2024}}

The genetic composition of the offspring depends on what type of automixis takes place. When endomitosis occurs before meiosisCosín, 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.{{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 |s2cid=19729047}} or when central fusion occurs (restitutional meiosis of anaphase I or the fusion of its products), the offspring get all{{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}} to more than half of the mother's genetic material and heterozygosity is mostly preserved{{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}} (if the mother has two alleles for a locus, the offspring will likely get both). This is because in anaphase I the homologous chromosomes are separated. Heterozygosity is not completely preserved when crossing over occurs in central fusion.{{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}} In the case of pre-meiotic doubling, recombination, if it happens, occurs between identical sister chromatids.

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.{{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 }} This is because at anaphase II the 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).{{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 chromosome during the parthenogenetic production of female and male aphids |journal=Genetics Research |volume=79 |issue=3 |pages=203–209 |pmid=12220127 |doi=10.1017/S0016672302005657 |doi-access=free}}

When meiosis is involved, the sex of the offspring depends on the type of sex determination system and the type of apomixis. In species that use the XY sex-determination system, parthenogenetic offspring have two X chromosomes and are female. In species that use the ZW sex-determination system the offspring genotype may be one of ZW (female), ZZ (male), or WW (non-viable in most species, 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). ZW offspring are produced by endoreplication before meiosis or by central fusion. ZZ and WW offspring occur either by terminal fusion or by endomitosis in the egg cell.{{cn|date=October 2024}}

In polyploid obligate parthenogens, like the whiptail lizard, all the offspring are female.

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.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}} Facultative parthenogenesis is extremely rare in nature, with only a few examples of animal taxa capable of facultative parthenogenesis. One of the best-known examples of taxa exhibiting facultative parthenogenesis are mayflies; presumably, this is the default reproductive mode of all species in this insect order.{{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}} 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 condors and the tropical lizard 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.{{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 |volume=112 |issue=7 |pages=569–574 |doi=10.1093/jhered/esab052 |pmc=8683835 |pmid=34718632}}

In aphids, a generation sexually conceived by a male and a female produces only females. The reason for this is the non-random segregation of the sex chromosomes 'X' and 'O' during spermatogenesis.{{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 }}

Facultative parthenogenesis is often used to describe cases of spontaneous parthenogenesis in normally sexual animals.{{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 |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 }} For example, many cases of spontaneous parthenogenesis in sharks, some snakes, Komodo dragons, and a variety of domesticated birds were widely attributed to facultative parthenogenesis.{{cite journal |last=Lampert |first=K.P. |year=2008 |title=Facultative parthenogenesis in vertebrates: Reproductive error or chance? |journal=Sexual Development |volume=2 |issue=6 |pages=290–301 |doi=10.1159/000195678 |pmid=19276631 |s2cid=9137566}} These cases are examples of spontaneous parthenogenesis. The occurrence of such asexually produced eggs in sexual animals can be explained by a meiotic error, leading to eggs produced via automixis.{{cite book |last1=Suomalainen |first1=E. |display-authors=etal |year=1987 |title=Cytology and Evolution in Parthenogenesis |place=Boca Raton, Florida |publisher=CRC Press}}

= Obligate =

Obligate parthenogenesis is the process in which organisms exclusively reproduce through asexual means.{{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 |volume=5 |issue=9 |pages=e12854 |doi=10.1371/journal.pone.0012854 |doi-access=free |pmid=20862222 |pmc=2942836 |bibcode=2010PLoSO...512854S }} 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.{{cite journal |last1=Scheuerl |first1=Thomas |display-authors=etal |year=2011 |title=Phenotypic of an allele causing obligate parthenogenesis |journal=Journal of Heredity |volume=102 |issue=4 |pages=409–415|doi=10.1093/jhered/esr036 |pmid=21576287 |pmc=3113615 }} web. {{nobr|23 October 2012}} 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), amphibians, and fishes in nature for which males are no longer a part of the reproductive process.{{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}} 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.

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.{{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 |volume=12 |issue=12 |pages=3493–3504 |doi=10.1046/j.1365-294X.2003.01998.x |pmid=14629364 |bibcode=2003MolEc..12.3493V |s2cid=32192796}}{{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 |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}} Relying solely on parthenogenetic reproduction has several advantages for an 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 species and the willow sawfly, Nematus oligospilus, which is sexual in its native Holarctic habitat but parthenogenetic where it has been introduced into the Southern Hemisphere.

Natural occurrence

Parthenogenesis does not apply to isogamous species.{{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 |pages=42}} Parthenogenesis occurs naturally in aphids, Daphnia, rotifers, nematodes, and some other invertebrates, as well as in many plants. Among vertebrates, strict parthenogenesis is only known to occur in lizards, snakes,{{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 |volume=1992 |issue=2 |pages=323–331|doi=10.2307/1446193 |jstor=1446193 }} birds,{{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 |volume=150 |issue=1 |pages=197–199 |doi=10.1111/j.1474-919x.2007.00755.x}} and sharks.{{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 |year=2007 |volume=3 |issue=4 |pages=425–427 |doi=10.1098/rsbl.2007.0189 |pmid=17519185 |pmc=2390672}} Fish, amphibians, and reptiles make use of various forms of gynogenesis and hybridogenesis (an incomplete form of parthenogenesis). The first all-female (unisexual) reproduction in vertebrates was described in the fish Poecilia formosa in 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 |volume=76 |issue=1983 |pages=628–630 |doi=10.1126/science.76.1983.628 |pmid=17730035 |bibcode=1932Sci....76..628H}} 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.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

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.{{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}} File:Parthenogenesis - Bischoff, Steve R 2010.tif

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.

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. 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 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.

Induced parthenogenesis of this type in mice and monkeys results in abnormal development. This is because mammals have imprinted 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 placental folding or interdigitation are one cause of swine parthenote abortive development.{{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 |volume=81 |issue=5 |pages=906–920 |year=2009 |pmid=19571260 |pmc=2770020 |doi=10.1095/biolreprod.109.078139}} As a consequence, research on the induced development of unfertilised eggs in humans is focused on the production of 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".

In humans

In 1955, Helen Spurway, a geneticist specializing in the reproductive biology of the guppy (Lebistes reticulatus), 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.Time, 28 November 1955; Editorial in The Lancet, 2: 967 (1955) 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.{{Cite journal |last1=Jose de Carli |first1=Gabriel |last2=Campos Pereira |first2=Tiago |date=September 2017 |title=On human parthenogenesis |url=https://linkinghub.elsevier.com/retrieve/pii/S0306987717302694 |journal=Medical Hypotheses |language=en |volume=106 |pages=57–60 |doi=10.1016/j.mehy.2017.07.008|pmid=28818272 |doi-access=free }} 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 cells) 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 (a child with two cell lineages in his body).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 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).

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 in the HLA region of DNA.{{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}} 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, it would be possible to generate a bank of cell lines whose tissue derivatives, collectively, could be MHC-matched with a significant number of individuals within the human population.{{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}}

After an independent investigation, it was revealed that the discredited South Korean scientist 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 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.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.

Similar phenomena

= 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 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 salamanders of the genus 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 is known to reproduce by gynogenesis.{{cite news |title=No sex for all-girl fish species |url=http://news.bbc.co.uk/2/hi/uk_news/scotland/edinburgh_and_east/7360770.stm |access-date=2007-06-11 |website=BBC News |date=23 April 2008}}

= Hybridogenesis =

File:Hybridogenesis in water frogs.gif (Pelophylax lessonae), marsh frog (P. ridibundus) and their hybrid – edible frog (P. kl. esculentus). On the left, primary hybridisation generating a hybrid, while the middle is the most widespread type of hybridogenesis.]]

Hybridogenesis is a mode of reproduction of hybrids. Hybridogenetic hybrids (for example AB genome), usually females, during gametogenesis exclude one of parental genomes (A) and produce gametes with unrecombined genome of second parental species (B), instead of containing mixed recombined parental genomes. First genome (A) is restored by fertilization of these gametes with gametes from the first species (AA, sexual host, usually male). Hybridogenesis is not completely asexual, but hemiclonal: half the genome is passed to the next generation clonally, unrecombined, intact (B), other half sexually, 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.

This form of reproduction is seen in some live-bearing fish of the genus Poeciliopsis as well as in some of the Pelophylax spp. ("green frogs" or "waterfrogs"):

P. kl. esculentus (edible frog): P. lessonae × P. ridibundus,
P. kl. grafi (Graf's hybrid frog): P. perezi × P. ridibundus
P. kl. hispanicus (Italian edible frog) – unknown origin: P. bergeri × P. ridibundus or P. kl. esculentus

Other examples where hybridogenesis is at least one of the modes of reproduction include i.e.,

Iberian minnow Tropidophoxinellus alburnoides (Squalius pyrenaicus × hypothetical ancestor related with Anaecypris hispanica)
spined loaches Cobitis hankugensis × C. longicorpus
Bacillus stick insects B. rossius × Bacillus grandii benazzii

In human culture

Parthenogenesis, in the form of reproduction from a single individual (typically a god), is common in mythology, religion, and folklore around the world, including in ancient Greek myth; for example, Athena was born from the head of Zeus.{{cite book |last1=Rigoglioso |first1=Marguerite |title=Virgin Mother Goddesses of Antiquity |date=2010 |publisher=Palgrave Macmillan |location=New York |isbn=978-0-230-61886-2}} {{clarify|date=February 2025}} In Christianity and Islam, there is the virgin birth of Jesus, and stories of miraculous births also appear in other global religions.{{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=978-9053565032 |page=1359}}

The theme is one of several aspects of reproductive biology explored in science fiction.{{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=9780860919933 |url=https://archive.org/details/alienzonecultura0000unse/page/215 }}

References

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}}

External links

[http://www.utexas.edu/research/crewslab/index.html Reproductive behavior in whiptails at Crews Laboratory]
[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]
[http://news.bbc.co.uk/2/hi/science/nature/6196225.stm "'Virgin births' for giant lizards (Komodo dragon)"] 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]

Category:Asexual reproduction in animals

Category:Zoology