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'{{Short description|Biological process}} [[File:Sexual cycle N-2N.svg |thumb |250px |In the first stage of sexual reproduction, [[meiosis]], the number of chromosomes is reduced from a [[diploid]] number (2n) to a [[haploid]] number (n). During [[fertilisation]], haploid gametes come together to form a diploid [[zygote]], and the original number of chromosomes is restored.]] '''Sexual reproduction''' is a type of lick lick lick lick I wanna eat yo dick but I can’t fuck up my nails so ima pick it up with chopsticks mouth wide open mouth wide open mouth widen like I was at the dentist mouth wide open mouth wide open put it so deep I can’t speak a sentence![[reproduction]] that involves a complex [[Biological life cycle|life cycle]] in which a [[gamete]] ([[haploid]] reproductive cells, such as a [[sperm]] or [[egg cell]]) with a single set of [[chromosome]]s combines with another gamete to produce a [[zygote]] that develops into an organism composed of [[Cell (biology)|cells]] with two sets of chromosomes ([[diploid]]).<ref>John Maynard Smith & Eörz Szathmáry, The Major Transitions in Evolution, [[W. H. Freeman and Company]], 1995, p 149</ref> This is typical in animals, though the number of chromosome sets and how that number changes in sexual reproduction varies, especially among plants, fungi, and other [[eukaryote]]s.<ref name="Chalker-2013" /><ref>{{Cite journal |last=Can Song |first=ShaoJun Liu |date=2012 |title=Polyploid Organisms |journal=Science China Life Sciences |volume=55 |issue=4 |pages=301–311 |doi=10.1007/s11427-012-4310-2 |pmid=22566086 |s2cid=17682966 |doi-access=free }}</ref> Sexual reproduction is the most common life cycle in [[multicellular organism|multicellular]] eukaryotes, such as [[animals]], [[fungi]] and [[plants]].<ref>{{Cite journal |last=Nieuwenhuis |first=Bart |date=October 19, 2016 |title=The frequency of sex in fungi |journal=Philosophical Transactions B |volume=371 |issue=1706 |doi=10.1098/rstb.2015.0540 |pmid=27619703 |pmc=5031624 }}</ref><ref>{{Cite web |last=Woods |first=Kerry |date=June 19, 2012 |title=Flowering Plants |url=https://eol.org/docs/discover/flowering-plants |access-date=September 12, 2022 |website=Encyclopedia of Life |archive-date=September 13, 2022 |archive-url=https://web.archive.org/web/20220913053019/https://eol.org/docs/discover/flowering-plants |url-status=live }}</ref> Sexual reproduction also occurs in some [[Unicellular organism|unicellular]] eukaryotes.<ref name="Chalker-2013">{{Cite journal |last=Chalker |first=Douglas |date=2013 |title=Epigenetics of Ciliates |url=https://cshperspectives.cshlp.org/content/5/12/a017764.full |journal=Cold Spring Harbor Perspectives in Biology |volume=5 |issue=12 |pages=a017764 |doi=10.1101/cshperspect.a017764 |pmid=24296171 |pmc=3839606 |via=Cold Spring Harbor |access-date=2022-09-13 |archive-date=2022-09-13 |archive-url=https://web.archive.org/web/20220913054521/https://cshperspectives.cshlp.org/content/5/12/a017764.full |url-status=live }}</ref><ref>{{Cite journal |last=Knop |first=Michael |date=2011 |title=Yeast cell morphology and sexual reproduction – A short overview and some considerations |url=https://www.sciencedirect.com/science/article/pii/S1631069111001405 |journal=Comptes Rendus Biologies |volume=334 |issue=8–9 |pages=599–606 |doi=10.1016/j.crvi.2011.05.007 |doi-broken-date=2024-03-22 |pmid=21819940 |via=Elsevier Science Direct |access-date=2022-09-13 |archive-date=2022-09-13 |archive-url=https://web.archive.org/web/20220913053019/https://www.sciencedirect.com/science/article/pii/S1631069111001405 |url-status=live }}</ref> Sexual reproduction does not occur in [[prokaryote]]s, unicellular organisms without [[cell nuclei]], such as [[bacteria]] and [[archaea]]. However, some processes in bacteria, including [[bacterial conjugation]], [[transformation (genetics)|transformation]] and [[transduction (genetics)|transduction]], may be considered analogous to sexual reproduction in that they incorporate new genetic information.<ref>{{Cite journal |last=Narra |first=Hema |date=September 5, 2015 |title=Of What Use Is Sex to Bacteria? |journal=Current Biology |volume=16 |issue=17 |pages=R705–R710 |doi=10.1016/j.cub.2006.08.024 |pmid=16950097 |s2cid=18268644 |doi-access=free }}</ref> Some [[protein]]s and other features that are key for sexual reproduction may have arisen in bacteria, but sexual reproduction is believed to have developed in an ancient eukaryotic ancestor.<ref>{{Cite journal |last=Goodenough |first=Ursula |date=March 1, 2014 |title=Origins of Eukaryotic Sexual Reproduction |journal=Cold Spring Harbor Perspectives in Biology |volume=6 |issue=3 |pages=a016154 |doi=10.1101/cshperspect.a016154 |pmid=24591519 |pmc=3949356 }}</ref> In eukaryotes, diploid precursor cells divide to produce haploid cells in a process called [[meiosis]]. In meiosis, DNA is replicated to produce a total of four copies of each chromosome. This is followed by two cell divisions to generate haploid gametes. After the DNA is replicated in meiosis, the [[homologous chromosome]]s pair up so that their [[DNA]] sequences are aligned with each other. During this period before cell divisions, genetic information is exchanged between homologous chromosomes in [[genetic recombination]]. Homologous chromosomes contain highly similar but not identical information, and by exchanging similar but not identical regions, genetic recombination increases genetic diversity among future generations.<ref name="Nature-2014">{{Cite web |date=2014 |title=DNA Is Constantly Changing through the Process of Recombination |url=https://www.nature.com/scitable/topicpage/dna-is-constantly-changing-through-the-process-6524876/#:~:text=Recombination%20occurs%20when%20two%20molecules,and%20swap%20segments%20of%20DNA. |access-date=September 14, 2022 |website=Nature |archive-date=September 15, 2022 |archive-url=https://web.archive.org/web/20220915062330/https://www.nature.com/scitable/topicpage/dna-is-constantly-changing-through-the-process-6524876/#:~:text=Recombination%20occurs%20when%20two%20molecules,and%20swap%20segments%20of%20DNA. |url-status=live }}</ref> During sexual reproduction, two haploid gametes combine into one diploid cell known as a [[zygote]] in a process called [[fertilisation|fertilization]]. The nuclei from the gametes fuse, and each gamete contributes half of the genetic material of the zygote. Multiple cell divisions by [[mitosis]] (without change in the number of chromosomes) then develop into a multicellular diploid phase or generation. In plants, the diploid phase, known as the [[sporophyte]], produces spores by meiosis. These spores then germinate and divide by mitosis to form a haploid multicellular phase, the [[gametophyte]], which produces gametes directly by mitosis. This type of life cycle, involving alternation between two multicellular phases, the sexual haploid gametophyte and asexual diploid sporophyte, is known as [[alternation of generations]]. The [[evolution of sexual reproduction]] is considered paradoxical,<ref>{{Cite web |last=Otto |first=Sarah |date=2014 |title=Sexual Reproduction and the Evolution of Sex |url=https://www.nature.com/scitable/topicpage/sexual-reproduction-and-the-evolution-of-sex-824 |access-date=28 Feb 2019 |website=Scitable |archive-date=28 January 2019 |archive-url=https://web.archive.org/web/20190128113746/http://www.nature.com/scitable/topicpage/sexual-reproduction-and-the-evolution-of-sex-824 |url-status=live }}</ref> because [[asexual reproduction]] should be able to outperform it as every young organism created can bear its own young. This implies that an asexual population has an intrinsic capacity to grow more rapidly with each generation.<ref name="maynard">[[John Maynard Smith]] ''The Evolution of Sex'' 1978.</ref> This 50% cost is a [[fitness (biology)|fitness]] disadvantage of sexual reproduction.<ref>Ridley, M. (2004) Evolution, 3rd edition. Blackwell Publishing, p. 314.</ref> The two-fold cost of sex includes this cost and the fact that any organism can only pass on 50% of its own genes to its offspring. However, one definite advantage of sexual reproduction is that it increases genetic diversity and impedes the accumulation of harmful genetic [[mutation]]s.<ref>{{Cite journal |doi=10.1038/ng.3216 |pmid=25685891 |date=4 March 2015 |url=https://www.ox.ac.uk/news/science-blog/making-sense-sex-why-genes-recombine |journal=Nature Genetics |title=Recombination affects accumulation of damaging and disease-associated mutations in human populations |last1=Hussin |first1=Julie G |last2=Hodgkinson |first2=Alan |last3=Idaghdour |first3=Youssef |last4=Grenier |first4=Jean-Christophe |last5=Goulet |first5=Jean-Philippe |last6=Gbeha |first6=Elias |last7=Hip-Ki |first7=Elodie |last8=Awadalla |first8=Philip |display-authors=3 |volume=47 |issue=4 |pages=400–404 |s2cid=24804649 |access-date=7 March 2021 |archive-date=20 January 2021 |archive-url=https://web.archive.org/web/20210120231628/https://www.ox.ac.uk/news/science-blog/making-sense-sex-why-genes-recombine |url-status=live }}</ref><ref name="Nature-2014" /> [[Sexual selection]] is a mode of [[natural selection]] in which some individuals out-reproduce others of a population because they are better at securing [[Mating|mates]] interest for sexual reproduction.<ref>{{cite book |author=Cecie Starr |title=[[Biology: The Unity and Diversity of Life]] |publisher=Cengage Learning |year=2013 |edition=Ralph Taggart, Christine Evers, Lisa Starr |page=281}}</ref>{{Failed verification|date=December 2023}}<ref name="PHYS-20140129">{{cite news |last=Vogt |first=Yngve |title=Large testicles are linked to infidelity |url=http://phys.org/news/2014-01-large-testicles-linked-infidelity.html |date=January 29, 2014 |work=[[Phys.org]] |access-date=January 31, 2014 |archive-date=November 12, 2020 |archive-url=https://web.archive.org/web/20201112041627/https://phys.org/news/2014-01-large-testicles-linked-infidelity.html |url-status=live }}</ref> It has been described as "a powerful evolutionary force that does not exist in asexual populations".<ref>{{cite journal |pmid=11395771 |year=2001 |last1=Agrawal |first1=A. F. |title=Sexual selection and the maintenance of sexual reproduction |journal=Nature |volume=411 |issue=6838 |pages=692–695 |doi=10.1038/35079590 |bibcode=2001Natur.411..692A |s2cid=4312385}}</ref> ==Evolution== {{Main|Evolution of sexual reproduction}} The first [[fossil]]ized evidence of sexual reproduction in eukaryotes is from the [[Stenian]] period, about 1.05 billion years old.<ref name=dateref>{{cite journal |author=N.J. Butterfield |year=2000 |title=Bangiomorpha pubescens n. gen., n. sp.: implications for the evolution of sex, multicellularity, and the Mesoproterozoic/Neoproterozoic radiation of eukaryotes |url=http://paleobiol.geoscienceworld.org/content/26/3/386.abstract |journal=[[Paleobiology (journal)|Paleobiology]] |volume=26 |issue=3 |pages=386–404 |doi=10.1666/0094-8373(2000)026<0386:BPNGNS>2.0.CO;2 |s2cid=36648568 |access-date=2013-11-03 |archive-date=2016-10-23 |archive-url=https://web.archive.org/web/20161023233131/http://paleobiol.geoscienceworld.org/content/26/3/386.abstract |url-status=live }}</ref><ref name="Gibson">{{cite journal |author=T.M. Gibson |year=2018 |title=Precise age of Bangiomorpha pubescens dates the origin of eukaryotic photosynthesis |url=https://pubs.geoscienceworld.org/gsa/geology/article/46/2/135/524864/Precise-age-of-Bangiomorpha-pubescens-dates-the |journal=[[Geology (journal)|Geology]] |volume=46 |issue=2 |pages=135–138 |doi=10.1130/G39829.1 |bibcode=2018Geo....46..135G |access-date=2021-10-28 |archive-date=2022-11-14 |archive-url=https://web.archive.org/web/20221114193201/https://pubs.geoscienceworld.org/gsa/geology/article/46/2/135/524864/Precise-age-of-Bangiomorpha-pubescens-dates-the |url-status=live }}</ref> Biologists studying [[evolution]] propose several explanations for the development of sexual reproduction and its maintenance. These reasons include reducing the likelihood of the [[Mullers ratchet|accumulation]] of deleterious mutations, increasing rate of [[red queen hypothesis|adaptation to changing environments]],<ref name=Gray2012>{{cite journal |last1=Gray |first1=J. C. |last2=Goddard |first2=M. R. |title=Gene-flow between niches facilitates local adaptation in sexual populations |journal=Ecology Letters |volume=15 |issue=9 |pages=955–962 |year=2012 |pmid=22690742 |doi=10.1111/j.1461-0248.2012.01814.x |bibcode=2012EcolL..15..955G |editor1-first=Michael |editor1-last=Bonsall }}</ref> [[tangled bank hypothesis|dealing with competition]], [[DNA repair]], masking deleterious mutations, and reducing genetic variation on the genomic level.<ref name="Michod">{{cite journal |last1=Michod |first1=R. E. |last2=Bernstein |first2=H. |last3=Nedelcu |first3=A. M. |title=Adaptive value of sex in microbial pathogens |journal=Infection, Genetics and Evolution |volume=8 |issue=3 |pages=267–285 |date=May 2008 |pmid=18295550 |doi=10.1016/j.meegid.2008.01.002 |url=http://www.hummingbirds.arizona.edu/Faculty/Michod/Downloads/IGE%20review%20sex.pdf |access-date=2013-04-22 |archive-date=2016-12-30 |archive-url=https://web.archive.org/web/20161230121043/http://www.hummingbirds.arizona.edu/Faculty/Michod/Downloads/IGE%20review%20sex.pdf |url-status=live }}</ref><ref name="Bernstein1" /><ref name="Bernstein2 "/><ref>{{cite journal |last1=Gorelick |first1=Root |title=Sex reduces genetic variation: a multidisciplinary review |journal=Evolution |volume=65 |issue=4 |pages=1088–1098 |pmid=21091466 |year=2010 |doi=10.1111/j.1558-5646.2010.01173.x |s2cid=7714974 |doi-access=free}}</ref> All of these ideas about why sexual reproduction has been maintained are generally supported, but ultimately the size of the population determines if sexual reproduction is entirely beneficial. Larger [[population]]s appear to respond more quickly to some of the benefits obtained through sexual reproduction than do smaller population sizes.<ref>{{cite journal |last1=Colegrave |first1=N. |title=Sex releases the speed limit on evolution |journal=Nature |year=2002 |volume=420 |issue=6916 |pages=664–6 |doi=10.1038/nature01191 |bibcode=2002Natur.420..664C |pmid=12478292 |hdl=1842/692 |s2cid=4382757 |hdl-access=free}}</ref> Maintenance of sexual reproduction has been explained by theories that work at several [[levels of selection]], though some of these models remain controversial.{{citation needed |date=September 2017}} However, newer models presented in recent years suggest a basic advantage for sexual reproduction in slowly reproducing [[complex organism]]s. Sexual reproduction allows these species to exhibit characteristics that depend on the specific [[Natural environment|environment]] that they inhabit, and the particular survival strategies that they employ.<ref>{{cite journal |doi=10.1007/s12064-009-0077-9 |title=Diploidy and the selective advantage for sexual reproduction in unicellular organisms |year=2009 |last1=Kleiman |first1=Maya |last2=Tannenbaum |first2=Emmanuel |journal=Theory in Biosciences |volume=128 |issue=4 |pages=249–85 |pmid=19902285 |arxiv=0901.1320 |s2cid=1179013}}</ref> ==Sexual selection== {{Main|Sexual selection}} In order to reproduce sexually, both males and females need to find a [[mating|mate]]. Generally in animals [[mate choice]] is made by females while males compete to be chosen. This can lead [[organism]]s to extreme efforts in order to reproduce, such as combat and display, or produce extreme features caused by a [[positive feedback]] known as a [[Fisherian runaway]]. Thus sexual reproduction, as a form of [[natural selection]], has an effect on [[evolution]]. [[Sexual dimorphism]] is where the basic [[phenotypic trait]]s vary between males and females of the same [[species]]. Dimorphism is found in both [[sex organ]]s and in [[secondary sex characteristics]], body size, physical strength and morphology, [[biological ornament]]ation, [[behavior]] and other bodily traits. However, sexual selection is only implied over an extended period of time leading to sexual dimorphism.<ref>Dimijian, G. G. (2005). Evolution of sexuality: biology and behavior. Proceedings (Baylor University. Medical Center), 18, 244–258.</ref> ==Animals== {{Further|Reproductive system#Animals |Fertilisation#Fertilisation in animals|Animal sexual behavior}} ===Arthropods=== {{excerpt |Arthropod |Reproduction and development}} ====Insects==== {{Further|Insect#Reproduction and development}} [[File:Australian Emperor mating and laying.jpg |thumb |250px |An [[Australian emperor |Australian emperor dragonfly]] laying eggs, guarded by a male]] Insect species make up more than two-thirds of all [[Extant taxon|extant]] animal species. Most insect species reproduce sexually, though some species are facultatively [[parthenogenetic]]. Many insects species have [[sexual dimorphism]], while in others the sexes look nearly identical. Typically they have two sexes with males producing spermatozoa and females ova. The ova develop into eggs that have a covering called the [[chorion]], which forms before internal fertilization. Insects have very diverse mating and reproductive strategies most often resulting in the male depositing [[spermatophore]] within the female, which she stores until she is ready for egg fertilization. After fertilization, and the formation of a zygote, and varying degrees of development, in many species the eggs are deposited outside the female; while in others, they develop further within the female and are born live.<ref name="Gullan and Cranston">{{cite book |last=Gullan |first=P. J. |author2=Cranston, P. S. |title=The Insects: An Outline of Entomology |publisher=Blackwell Publishing |location=Oxford |year=2005 |edition=3rd |isbn=978-1-4051-1113-3 |url=https://archive.org/details/isbn_9781405111133 |pages=129–143}}</ref> ===Mammals=== {{Main|Mammalian reproduction}} {{See also |Human reproduction}} There are three extant kinds of mammals: [[monotreme]]s, [[placental]]s and [[marsupial]]s, all with internal fertilization. In placental mammals, offspring are born as juveniles: complete animals with the [[sex organ]]s present although not reproductively functional. After several months or years, depending on the species, the sex organs develop further to maturity and the animal becomes [[Sexual maturity|sexually mature]]. Most female mammals are only [[fertility|fertile]] during certain periods during their [[estrous]] cycle, at which point they are ready to mate. Individual male and female mammals meet and carry out [[animal sexual behavior#Mammals|copulation]].<ref name="NYT-20240213">{{cite news |last=Preston |first=Elizabeth |title=Self-Love Is Important, but We Mammals Are Stuck With Sex - 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 |date=13 February 2024 |work=[[The New York Times]] |url-status=live |archiveurl=https://archive.today/20240213114627/https://www.nytimes.com/2024/02/13/science/valentines-day-sexual-reproduction-parthenogenesis.html |archivedate=13 February 2024 |accessdate=16 February 2024 }}</ref> For most mammals, males and females [[Promiscuity|exchange sexual partners throughout their adult lives]].<ref>{{cite journal |last=Reichard |first=U.H. |title=Monogamy—A variable relationship |journal=Max Planck Research |volume=3 |pages=62–7 |year=2002 |url=http://www.mpg.de/1028786/W001_Biology-Medicine_062_067.pdf |archive-url=https://web.archive.org/web/20130524204835/http://www.mpg.de/1028786/W001_Biology-Medicine_062_067.pdf |archive-date=24 May 2013 |access-date=24 April 2013 }}</ref><ref name="Barash, Lipton, 2001">{{cite book |last1=Lipton |first1=Judith Eve |last2=Barash |first2=David P. |title=The Myth of Monogamy: Fidelity and Infidelity in Animals and People |publisher=W.H. Freeman and Company |location=San Francisco |year=2001 |isbn=0-7167-4004-4 |url=https://archive.org/details/isbn_9780716740049 }}</ref><ref name="Gowaty, Morell, 1998">Research conducted by [[Patricia Adair Gowaty]]. Reported by {{cite journal |last=Morell |first=V. |year=1998 |title=Evolution of sex: A new look at monogamy |journal=Science |volume=281 |pages=1982–1983 |issue=5385 |doi=10.1126/science.281.5385.1982 |pmid=9767050 |s2cid=31391458 }}</ref> ===Fish=== {{Further|Fish#Reproductive system}} The vast majority of fish species lay eggs that are then fertilized by the male.<ref>{{Cite web |url=http://www.seaworld.org/animal-info/info-books/bony-fish/reproduction.htm |title=BONY FISHES – Reproduction |access-date=2008-02-11 |archive-date=2013-10-03 |archive-url=https://web.archive.org/web/20131003122913/http://www.seaworld.org/animal-info/info-books/bony-fish/reproduction.htm }}</ref> Some species lay their eggs on a substrate like a rock or on plants, while others scatter their eggs and the eggs are fertilized as they drift or sink in the water column. Some fish species use internal fertilization and then disperse the developing eggs or give birth to live offspring. Fish that have live-bearing offspring include the [[guppy]] and mollies or ''[[Poecilia]]''. Fishes that give birth to live young can be [[ovoviviparous]], where the eggs are fertilized within the female and the eggs simply hatch within the female body, or in [[seahorse]]s, the male carries the developing young within a pouch, and gives birth to live young.<ref name=Cavendish2001>{{Cite book |author=M. Cavendish |year=2001 |title=Endangered Wildlife and Plants of the World |url=https://books.google.com/books?id=s5zZJVu2hxYC&pg=PA1254 |page=1252 |isbn=978-0-7614-7194-3 |publisher=Marshall Cavendish |access-date=2013-11-03 }}</ref> Fishes can also be [[viviparous]], where the female supplies nourishment to the internally growing offspring. Some fish are [[hermaphrodite]]s, where a single fish is both male and female and can produce eggs and sperm. In hermaphroditic fish, some are male and female at the same time while in other fish they are serially hermaphroditic; starting as one sex and changing to the other. In at least one hermaphroditic species, self-fertilization occurs when the eggs and sperm are released together. Internal self-fertilization may occur in some other species.<ref>{{cite journal |last1=Orlando |first1=EF |last2=Katsu |first2=Y |last3=Miyagawa |first3=S |last4=Iguchi |first4=T |year=2006 |title=Cloning and differential expression of estrogen receptor and aromatase genes in the self-fertilizing hermaphrodite and male mangrove rivulus, Kryptolebias marmoratus |journal=[[Journal of Molecular Endocrinology]] |volume=37 |issue=2 |pages=353–365 |doi=10.1677/jme.1.02101 |pmid=17032750 |doi-access=free }}</ref> One fish species does not reproduce by sexual reproduction but uses sex to produce offspring; ''[[Poecilia formosa]]'' is a unisex species that uses a form of [[parthenogenesis]] called [[gynogenesis]], where unfertilized eggs develop into embryos that produce female offspring. ''Poecilia formosa'' mate with males of other fish species that use internal fertilization, the sperm does not fertilize the eggs but stimulates the growth of the eggs which develops into embryos.<ref>{{cite journal |last1=Schlupp |first1=I. |last2=Parzefall |first2=J. |last3=Epplen |first3=J. T. |last4=Schartl |first4=M. |title=Limia vittata as host species for the Amazon molly: no evidence for sexual reproduction |journal=Journal of Fish Biology |publisher=Wiley |volume=48 |issue=4 |year=1996 |issn=0022-1112 |doi=10.1111/j.1095-8649.1996.tb01472.x |pages=792–795|bibcode=1996JFBio..48..792S }}</ref> ==Plants== {{Main|Plant reproduction}} Animals have life cycles with a single diploid multicellular phase that produces haploid gametes directly by meiosis. Male gametes are called sperm, and female gametes are called eggs or ova. In animals, fertilization of the ovum by a sperm results in the formation of a diploid zygote that develops by repeated mitotic divisions into a diploid adult. Plants have two multicellular life-cycle phases, resulting in an [[alternation of generations]]. Plant zygotes germinate and divide repeatedly by mitosis to produce a diploid multicellular organism known as the sporophyte. The mature sporophyte produces haploid spores by meiosis that germinate and divide by mitosis to form a multicellular gametophyte phase that produces gametes at maturity. The gametophytes of different groups of plants vary in size. Mosses and other pteridophytic plants may have gametophytes consisting of several million cells, while [[angiosperm]]s have as few as three cells in each pollen grain. ===Flowering plants=== [[File:hosta3.jpg|thumb|Flowers contain the sexual organs of flowering plants.]] [[Flowering plant]]s are the dominant plant form on land<ref name=Judd>{{cite book |first1=Walter S. |last1=Judd |first2=Christopher S. |last2=Campbell |first3=Elizabeth A. |last3=Kellogg |first4=Peter F. |last4=Stevens |first5=Michael J. |last5=Donoghue |title=Plant systematics, a phylogenetic approach |edition=2 |date=2002 |publisher=Sinauer Associates |location=Sunderland, Massachusetts |isbn=0-87893-403-0 }}</ref>{{rp |168, 173}} and they reproduce either sexually or asexually. Often their most distinguishing feature is their reproductive organs, commonly called flowers. The [[Stamen|anther]] produces [[pollen |pollen grains]] which contain the male [[gametophyte]]s that produce sperm nuclei. For pollination to occur, pollen grains must attach to the stigma of the female reproductive structure ([[carpel]]), where the female gametophytes are located within ovules enclose within the [[ovary]]. After the pollen tube grows through the carpel's style, the [[sex]] cell nuclei from the pollen grain migrate into the ovule to fertilize the egg cell and endosperm nuclei within the female gametophyte in a process termed [[double fertilization]]. The resulting zygote develops into an embryo, while the triploid endosperm (one sperm cell plus two female cells) and female tissues of the ovule give rise to the surrounding tissues in the developing seed. The ovary, which produced the female gametophyte(s), then grows into a [[fruit]], which surrounds the seed(s). Plants may either [[Self-pollination|self-pollinate]] or [[pollination|cross-pollinate]]. In 2013, flowers dating from the [[Cretaceous]] (100&nbsp;million years before present) were found encased in amber, the oldest evidence of sexual reproduction in a flowering plant. Microscopic images showed tubes growing out of pollen and penetrating the flower's stigma. The pollen was sticky, suggesting it was carried by insects.<ref>{{cite journal |first1=George O. Jr. |last1=Poinar |first2=Kenton L. |last2=Chambers |first3=Joerg |last3=Wunderlich |title=Micropetasos, a new genus of angiosperms from mid-Cretaceous Burmese amber |journal=Journal of the Botanical Research Institute of Texas |volume=7 |issue=2 |pages=745–750 |date=10 December 2013 |url=http://brit.org/webfm_send/455 |archive-url=https://web.archive.org/web/20140105073839/http://brit.org/webfm_send/455 |archive-date=5 January 2014 }}</ref> ===Ferns=== {{further|Alternation of generations}} Ferns produce large diploid [[sporophyte]]s with [[rhizome]]s, roots and leaves. Fertile leaves produce [[sporangia]] that contain haploid [[spore]]s. The spores are released and germinate to produce small, thin gametophytes that are typically heart shaped and green in color. The gametophyte [[Prothallus|prothalli]], produce motile sperm in the [[antheridia]] and egg cells in [[archegonia]] on the same or different plants.<ref>{{cite web |title=Fern Reproduction |url=https://www.fs.usda.gov/wildflowers/beauty/ferns/reproduction.shtml |publisher=U.S. Forest Service |access-date=24 April 2023 |archive-date=24 April 2023 |archive-url=https://web.archive.org/web/20230424091540/https://www.fs.usda.gov/wildflowers/beauty/ferns/reproduction.shtml |url-status=live }}</ref> After rains or when dew deposits a film of water, the motile sperm are splashed away from the antheridia, which are normally produced on the top side of the thallus, and swim in the film of water to the archegonia where they fertilize the egg. To promote out crossing or cross fertilization the sperm are released before the eggs are receptive of the sperm, making it more likely that the sperm will fertilize the eggs of different thallus. After fertilization, a [[zygote]] is formed which grows into a new sporophytic plant. The condition of having separate sporophyte and gametophyte plants is called [[alternation of generation]]s. ===Bryophytes=== The [[bryophyte]]s, which include [[Marchantiophyta|liverwort]]s, [[hornwort]]s and [[moss]]es, reproduce both sexually and [[Vegetative reproduction|vegetatively]]. They are small plants found growing in moist locations and like ferns, have motile sperm with [[flagella]] and need water to facilitate sexual reproduction. These plants start as a haploid spore that grows into the dominant gametophyte form, which is a multicellular haploid body with leaf-like structures that [[photosynthesis|photosynthesize]]. Haploid gametes are produced in antheridia (male) and archegonia (female) by mitosis. The sperm released from the antheridia respond to chemicals released by ripe archegonia and swim to them in a film of water and fertilize the egg cells thus producing a zygote. The [[zygote]] divides by mitotic division and grows into a multicellular, diploid sporophyte. The sporophyte produces spore capsules ([[sporangia]]), which are connected by stalks ([[seta]]e) to the archegonia. The spore capsules produce spores by meiosis and when ripe the capsules burst open to release the spores. Bryophytes show considerable variation in their reproductive structures and the above is a basic outline. Also in some species each plant is one sex ([[dioicous]]) while other species produce both sexes on the same plant ([[monoicous]]).<ref>{{cite book |first1=Jon Lovett |last1=Doust |first2=Lesley Lovett |last2=Doust |year=1988 |title=Plant Reproductive Ecology: Patterns and Strategies |publisher=[[Oxford University Press]] |page=290 |isbn=978-0-19-506394-3 }}</ref> ==Fungi== {{Main|Mating in fungi}} {{Further|Fungus#Reproduction}} [[File:Puffballs emitting spores.jpg |thumb|Puffballs emitting spores]] [[Fungi]] are classified by the methods of sexual reproduction they employ. The outcome of sexual reproduction most often is the production of [[resting spore]]s that are used to survive inclement times and to spread. There are typically three phases in the sexual reproduction of fungi: [[plasmogamy]], [[karyogamy]] and [[meiosis]]. The cytoplasm of two parent cells fuse during plasmogamy and the nuclei fuse during karyogamy. New haploid gametes are formed during meiosis and develop into spores. The adaptive basis for the maintenance of sexual reproduction in the [[Ascomycota]] and [[Basidiomycota]] ([[dikaryon]]) [[fungus|fungi]] was reviewed by Wallen and Perlin.<ref name="pmid29619017">{{cite journal |last1=Wallen |first1=R. M. |last2=Perlin |first2=M. H. |title=An Overview of the Function and Maintenance of Sexual Reproduction in Dikaryotic Fungi |journal=Front Microbiol |volume=9 |page=503 |year=2018 |pmid=29619017 |pmc=5871698 |doi=10.3389/fmicb.2018.00503 |doi-access=free }}</ref> They concluded that the most plausible reason for maintaining this capability is the benefit of [[DNA repair|repairing DNA damage]], caused by a variety of stresses, through [[homologous recombination|recombination]] that occurs during [[meiosis]].<ref name="pmid29619017" /> ==Bacteria and archaea== Three distinct processes in [[prokaryote]]s are regarded as similar to [[Origin and function of meiosis|eukaryotic sex]]: [[bacterial transformation]], which involves the incorporation of foreign DNA into the bacterial chromosome; [[bacterial conjugation]], which is a transfer of [[plasmid]] DNA between bacteria, but the plasmids are rarely incorporated into the bacterial chromosome; and [[Prokaryote#DNA transfer|gene transfer and genetic exchange in archaea]]. Bacterial transformation involves the [[genetic recombination|recombination of genetic material]] and its function is mainly associated with [[Sexual recombination#Recombinational repair|DNA repair]]. Bacterial transformation is a complex process encoded by numerous bacterial genes, and is a bacterial adaptation for DNA transfer.<ref name="Michod"/><ref name="Bernstein1">{{cite journal |doi=10.1525/bio.2010.60.7.5 |title=Evolutionary Origin of Recombination during Meiosis |year=2010 |last1=Bernstein |first1=Harris |last2=Bernstein |first2=Carol |journal=BioScience |volume=60 |issue=7 |pages=498–505 |s2cid=86663600}}</ref> This process occurs naturally in at least 40 bacterial species.<ref>{{cite journal |pmid=7968924 |year=1994 |last1=Lorenz |first1=M.G. |last2=Wackernagel |first2=W. |title=Bacterial gene transfer by natural genetic transformation in the environment |volume=58 |issue=3 |pages=563–602 |pmc=372978 |journal=Microbiological Reviews |doi=10.1128/mmbr.58.3.563-602.1994}}</ref> For a bacterium to bind, take up, and recombine exogenous DNA into its chromosome, it must enter a special physiological state referred to as competence (see [[Natural competence]]). Sexual reproduction in early single-celled eukaryotes may have evolved from bacterial transformation,<ref name="Bernstein2">Bernstein, H.; Bernstein, C.; Michod, R. E. (2012) "[https://www.novapublishers.com/catalog/product_info.php?products_id=31918 DNA Repair as the Primary Adaptive Function of Sex in Bacteria and Eukaryotes] {{Webarchive |url=https://web.archive.org/web/20131029202307/https://www.novapublishers.com/catalog/product_info.php?products_id=31918 |date=2013-10-29 }}". Chapter 1, pp. 1–50, in ''DNA Repair: New Research'', Editors S. Kimura and Shimizu S. Nova Sci. Publ., Hauppauge, New York. Open access for reading only. {{ISBN |978-1-62100-756-2}}</ref> or from a similar process in [[archaea]] (see below). On the other hand, bacterial conjugation is a type of direct transfer of DNA between two bacteria mediated by an external appendage called the conjugation pilus.<ref>{{cite journal |pmid=22986519 |year=2012 |last1=Lodé |first1=T. |title=Have Sex or Not? Lessons from Bacteria |doi=10.1159/000342879 |journal=Sexual Development |volume=6 |issue=6 |pages=325–328 |doi-access=free}}</ref> Bacterial conjugation is controlled by [[plasmid |plasmid genes]] that are adapted for spreading copies of the plasmid between bacteria. The infrequent integration of a plasmid into a host bacterial chromosome, and the subsequent transfer of a part of the host chromosome to another cell do not appear to be bacterial adaptations.<ref name="Michod" /><ref>{{cite book |last1=Krebs |first1=J. E. |last2=Goldstein |first2=E. S. |last3=Kilpatrick |first3=ST |year=2011 |title=Lewin's GENES X |pages=[https://archive.org/details/lewinsgenesx0000unse/page/289 289–292] |publisher=Jones and Bartlett Publishers |location=Boston |isbn=978-0-7637-6632-0 |url=https://archive.org/details/lewinsgenesx0000unse/page/289}}</ref> Exposure of hyperthermophilic archaeal Sulfolobus species to DNA damaging conditions induces cellular aggregation accompanied by high frequency [[genetic marker]] exchange<ref>{{cite journal |last1=Fröls |first1=Sabrina |last2=Ajon |first2=Malgorzata |last3=Wagner |first3=Michaela |last4=Teichmann |first4=Daniela |last5=Zolghadr |first5=Behnam |last6=Folea |first6=Mihaela |last7=Boekema |first7=Egbert J. |last8=Driessen |first8=Arnold J. M. |last9=Schleper |first9=Christa |last10=Albers |first10=Sonja-Verena |display-authors=3 |title=UV-inducible cellular aggregation of the hyperthermophilic archaeon Sulfolobus solfataricus is mediated by pili formation |journal=Molecular Microbiology |publisher=Wiley |volume=70 |issue=4 |date=9 October 2008 |issn=0950-382X |doi=10.1111/j.1365-2958.2008.06459.x |pages=938–952 |pmid=18990182 |s2cid=12797510 |doi-access=free }}</ref><ref name="Ajon">{{cite journal |last1=Ajon |first1=Małgorzata |last2=Fröls |first2=Sabrina |last3=van Wolferen |first3=Marleen |last4=Stoecker |first4=Kilian |last5=Teichmann |first5=Daniela |last6=Driessen |first6=Arnold J. M. |last7=Grogan |first7=Dennis W. |last8=Albers |first8=Sonja-Verena |last9=Schleper |first9=Christa |display-authors=3 |title=UV-inducible DNA exchange in hyperthermophilic archaea mediated by type IV pili |journal=Molecular Microbiology |publisher=Wiley |volume=82 |issue=4 |date=18 October 2011 |issn=0950-382X |doi=10.1111/j.1365-2958.2011.07861.x |pages=807–817 |pmid=21999488 |s2cid=42880145 |url=https://pure.rug.nl/ws/files/6771142/2011MolMicrobiolAjon.pdf |access-date=13 December 2019 |archive-date=10 October 2021 |archive-url=https://web.archive.org/web/20211010101112/https://pure.rug.nl/ws/files/6771142/2011MolMicrobiolAjon.pdf |url-status=live }}</ref> Ajon et al.<ref name=Ajon /> hypothesized that this cellular aggregation enhances species-specific DNA repair by homologous recombination. DNA transfer in ''Sulfolobus'' may be an early form of sexual interaction similar to the more well-studied bacterial transformation systems that also involve species-specific DNA transfer leading to homologous recombinational repair of DNA damage. ==See also== {{div col |colwidth=30em}} * [[Amphimixis (psychology)]] * [[Anisogamy]] * [[Biological reproduction]] * [[Hermaphroditism]] * [[Isogamy]] * [[Mate choice]] * [[Mating in fungi]] * [[Operational sex ratio]] * [[Outcrossing]] * [[Allogamy]] * [[Self-incompatibility]] * [[Sex]] * [[Sexual intercourse]] * [[Transformation (genetics)]] {{div col end}} ==References== {{reflist|colwidth=30em}} ==Further reading== * Pang, K. "Certificate Biology: New Mastering Basic Concepts", Hong Kong, 2004 * [http://www.biolreprod.org/ Journal of Biology of Reproduction], accessed in August 2005. * [https://www.sciencedaily.com/releases/2003/02/030203071703.htm "Sperm Use Heat Sensors To Find The Egg; Weizmann Institute Research Contributes To Understanding Of Human Fertilization"], ''Science Daily'', 3 February 2003 * {{cite book |editor-last=Michod |editor1-first=R. E. |editor2-last=Levin |editor2-first=B.E. |year=1987 |title=The Evolution of sex: An examination of current ideas |publisher=Sinauer Associates |location=Sunderland, Massachusetts |isbn=978-0-87893-458-4 |url-access=registration |url=https://archive.org/details/evolutionofsexex0000unse |ref=none}} * {{cite book |last=Michod |first=R. E. |title=Eros and Evolution: A Natural Philosophy of Sex |year=1994 |publisher=Perseus Books |isbn=978-0-201-40754-9 |url=https://archive.org/details/erosevolutionnat0000mich |ref=none}} ==External links== * [https://www.youtube.com/watch?v=kaSIjIzAtYA Khan Academy, video lecture] * [https://www.nature.com/scitable/topicpage/sexual-reproduction-and-the-evolution-of-sex-824/ Sexual Reproduction and the Evolution of Sex] ([https://archive.today/20231008141323/https://www.nature.com/scitable/topicpage/sexual-reproduction-and-the-evolution-of-sex-824/ Archived (2023)]) − [[Nature (journal)|Nature journal]] (2008) {{Sex (biology)}} {{Animal sexual behavior}} {{Portal bar |Biology |evolutionary biology |Science}} {{Authority control}} [[Category:Sexual reproduction| ]] [[Category:Developmental biology]] [[Category:Fertility]] [[Category:Reproduction]] [[Category:Sexuality]]'