Editing Mating system (section)

==In microorganisms==

===Bacteria===

Mating in [[bacteria]] involves transfer of DNA from one cell to another and incorporation of the transferred DNA into the recipient bacteria's [[genome]] by [[homologous recombination]].  Transfer of DNA between bacterial cells can occur in three main ways.  First, a bacterium can take up [[exogenous DNA]] released into the intervening medium from another bacterium by a process called [[Transformation (genetics)|'''transformation''']].  DNA can also be transferred from one bacterium to another by the process of [[Transduction (genetics)|'''transduction''']], which is mediated by an infecting virus (bacteriophage).  The third method of DNA transfer is [[Bacterial conjugation|''conjugation'']], in which a [[plasmid]] mediates transfer through direct cell contact between cells.

Transformation, unlike transduction or conjugation, depends on numerous bacterial gene products that specifically interact to perform this complex process,<ref name="pmid15083159">{{cite journal |vauthors=Chen I, Dubnau D |title=DNA uptake during bacterial transformation |journal=Nat. Rev. Microbiol. |volume=2 |issue=3 |pages=241–9 |year=2004 |pmid=15083159 |doi=10.1038/nrmicro844 |s2cid=205499369 }}</ref> and thus transformation is clearly a bacterial [[adaptation]] for DNA transfer.  In order for a bacterium to bind, take up and recombine donor DNA into its own chromosome, it must first enter a special physiological state termed [[natural competence]].  In ''[[Bacillus subtilis]]'' about 40 genes are required for the development of competence and DNA uptake.<ref name="pmid8901420">{{cite journal |vauthors=Solomon JM, Grossman AD |title=Who's competent and when: regulation of natural genetic competence in bacteria |journal=Trends Genet. |volume=12 |issue=4 |pages=150–5 |year=1996 |pmid=8901420 |doi= 10.1016/0168-9525(96)10014-7}}</ref>  The length of DNA transferred during ''B. subtilis'' transformation can be as much as a third and up to the whole chromosome.<ref name="pmid11388459">{{cite journal |vauthors=Akamatsu T, Taguchi H |title=Incorporation of the whole chromosomal DNA in protoplast lysates into competent cells of Bacillus subtilis |journal=Biosci. Biotechnol. Biochem. |volume=65 |issue=4 |pages=823–9 |year=2001 |pmid=11388459 |doi=10.1271/bbb.65.823 |s2cid=30118947 |doi-access=free }}</ref><ref name="pmid16716928">{{cite journal |vauthors=Saito Y, Taguchi H, Akamatsu T |title=Fate of transforming bacterial genome following incorporation into competent cells of Bacillus subtilis: a continuous length of incorporated DNA |journal=J. Biosci. Bioeng. |volume=101 |issue=3 |pages=257–62 |year=2006 |pmid=16716928 |doi=10.1263/jbb.101.257 }}</ref>  Transformation appears to be common among bacterial species, and at least 60 species are known to have the natural ability to become competent for transformation.<ref name="pmid17997281">{{cite journal |vauthors=Johnsborg O, Eldholm V, Håvarstein LS |title=Natural genetic transformation: prevalence, mechanisms and function |journal=Res. Microbiol. |volume=158 |issue=10 |pages=767–78 |year=2007 |pmid=17997281 |doi=10.1016/j.resmic.2007.09.004 |doi-access=free }}</ref>  The development of competence in nature is usually associated with stressful environmental conditions, and seems to be an adaptation for facilitating repair of DNA damage in recipient cells.<ref>Bernstein H, Bernstein C, Michod RE (2012). DNA repair as the primary adaptive function of sex in bacteria and eukaryotes.  Chapter 1: pp.1-49 in: DNA Repair: New Research, Sakura Kimura and Sora Shimizu editors. Nova Sci. Publ., Hauppauge, N.Y.  {{ISBN|978-1-62100-808-8}} https://www.novapublishers.com/catalog/product_info.php?products_id=31918 {{Webarchive|url=https://web.archive.org/web/20131029202307/https://www.novapublishers.com/catalog/product_info.php?products_id=31918 |date=2013-10-29 }}</ref>

===Archaea===

In several species of [[archaea]], mating is mediated by formation of cellular aggregates.
''[[Halobacterium]] volcanii'', an extreme [[Halophile|halophilic]] archaeon, forms cytoplasmic bridges between cells that appear to be used for transfer of DNA from one cell to another in either direction.<ref name="pmid2818746">{{cite journal |vauthors=Rosenshine I, Tchelet R, Mevarech M |title=The mechanism of DNA transfer in the mating system of an archaebacterium |journal=Science |volume=245 |issue=4924 |pages=1387–9 |year=1989 |pmid=2818746 |doi= 10.1126/science.2818746|bibcode=1989Sci...245.1387R }}</ref>

When the [[Hyperthermophile|hyperthermophilic]] archaea ''[[Sulfolobus solfataricus]]''<ref name=Frol>{{cite journal |vauthors=Fröls S, Ajon M, Wagner M, Teichmann D, Zolghadr B, Folea M, Boekema EJ, Driessen AJ, Schleper C, Albers SV |title=UV-inducible cellular aggregation of the hyperthermophilic archaeon Sulfolobus solfataricus is mediated by pili formation |journal=Mol. Microbiol. |volume=70 |issue=4 |pages=938–52 |year=2008 |pmid=18990182 |doi=10.1111/j.1365-2958.2008.06459.x |url=https://www.rug.nl/research/portal/files/56956856/UV_inducible_cellular_aggregation_of_the_hyperthermophilic_archaeon_Sulfolobus_solfataricus_is_mediated_by_pili_formation.pdf|doi-access=free }}</ref> and ''[[Sulfolobus acidocaldarius]]''<ref name=Ajon>{{cite journal |vauthors=Ajon M, Fröls S, van Wolferen M, Stoecker K, Teichmann D, Driessen AJ, Grogan DW, Albers SV, Schleper C |title=UV-inducible DNA exchange in hyperthermophilic archaea mediated by type IV pili |journal=Mol. Microbiol. |volume=82 |issue=4 |pages=807–17 |year=2011 |pmid=21999488 |doi=10.1111/j.1365-2958.2011.07861.x |url=https://pure.rug.nl/ws/files/6771142/2011MolMicrobiolAjon.pdf|doi-access=free }}</ref> are exposed to the DNA damaging agents [[Ultraviolet|UV]] irradiation, [[bleomycin]] or [[Mitomycins|mitomycin C]], species-specific cellular aggregation is induced.  Aggregation in ''S. solfataricus'' could not be induced by other physical stressors, such as pH or temperature shift,<ref name=Frol /> suggesting that aggregation is induced specifically by DNA damage.  Ajon et al.<ref name=Ajon /> showed that UV-induced cellular aggregation mediates chromosomal marker exchange with high frequency in ''S. acidocaldarius''.  Recombination rates exceeded those of uninduced cultures by up to three orders of magnitude.  Frols et al.<ref name=Frol /> and Ajon et al.<ref name=Ajon /> hypothesized that cellular aggregation enhances species-specific DNA transfer between ''Sulfolobus'' cells in order to provide increased repair of damaged DNA by means of [[homologous recombination]]. This response appears to be a primitive form of sexual interaction similar to the more well-studied bacterial transformation systems that are also associated with species specific DNA transfer between cells leading to homologous recombinational repair of DNA damage.{{Citation needed|date=December 2019|reason=removed citation to predatory publisher content}}

===Protists===

Protists are a large group of diverse [[Eukaryote|eukaryotic]] [[microorganism]]s, mainly [[Unicellular organism|unicellular]] animals and plants, that do not form [[Tissue (biology)|tissues]]. Eukaryotes emerged in evolution more than 1.5 billion years ago.<ref name="pmid11452306">{{cite journal |vauthors=Javaux EJ, Knoll AH, Walter MR |title=Morphological and ecological complexity in early eukaryotic ecosystems |journal=Nature |volume=412 |issue=6842 |pages=66–9 |year=2001 |pmid=11452306 |doi=10.1038/35083562 |bibcode=2001Natur.412...66J |s2cid=205018792 }}</ref> The earliest eukaryotes were likely protists.  Mating and [[sexual reproduction]] are widespread among extant eukaryotes. Based on a phylogenetic analysis, Dacks and Roger<ref name="pmid10229582">{{cite journal |vauthors=Dacks J, Roger AJ |title=The first sexual lineage and the relevance of facultative sex |journal=J. Mol. Evol. |volume=48 |issue=6 |pages=779–83 |year=1999 |pmid=10229582 |doi= 10.1007/pl00013156|bibcode=1999JMolE..48..779D |s2cid=9441768 }}</ref> proposed that facultative sex was present in the common ancestor of all eukaryotes.

However, to many biologists it seemed unlikely until recently, that mating and sex could be a primordial and fundamental characteristic of eukaryotes. A principal reason for this view was that mating and sex appeared to be lacking in certain [[pathogen]]ic protists whose ancestors branched off early from the eukaryotic family tree.  However, several of these protists are now known to be capable of, or to recently have had, the capability for [[meiosis]] and hence mating. To cite one example, the common intestinal parasite ''[[Giardia lamblia|Giardia intestinalis]]'' was once considered to be a descendant of a protist lineage that predated the emergence of meiosis and sex.  However, ''G. intestinalis'' was recently found to have a core set of genes that function in meiosis and that are widely present among sexual eukaryotes.<ref name="pmid15668177">{{cite journal |vauthors=Ramesh MA, Malik SB, Logsdon JM |title=A phylogenomic inventory of meiotic genes; evidence for sex in Giardia and an early eukaryotic origin of meiosis |journal=Curr. Biol. |volume=15 |issue=2 |pages=185–91 |year=2005 |pmid=15668177 |doi=10.1016/j.cub.2005.01.003 |s2cid=17013247 |doi-access=free |bibcode=2005CBio...15..185R }}</ref> These results suggested that ''G. intestinalis'' is capable of meiosis and thus mating and sexual reproduction. Furthermore, direct evidence for meiotic recombination, indicative of mating and sexual reproduction, was also found in ''G. intestinalis''.<ref name="pmid17980591">{{cite journal |vauthors=Cooper MA, Adam RD, Worobey M, Sterling CR |title=Population genetics provides evidence for recombination in Giardia |journal=Curr. Biol. |volume=17 |issue=22 |pages=1984–8 |year=2007 |pmid=17980591 |doi=10.1016/j.cub.2007.10.020 |s2cid=15991722 |doi-access=free |bibcode=2007CBio...17.1984C }}</ref> Other protists for which evidence of mating and sexual reproduction has recently been described are parasitic protozoa of the genus ''[[Leishmania]]'',<ref name="pmid19359589">{{cite journal |vauthors=Akopyants NS, Kimblin N, Secundino N, Patrick R, Peters N, Lawyer P, Dobson DE, Beverley SM, Sacks DL |title=Demonstration of genetic exchange during cyclical development of Leishmania in the sand fly vector |journal=Science |volume=324 |issue=5924 |pages=265–8 |year=2009 |pmid=19359589 |pmc=2729066 |doi=10.1126/science.1169464 |bibcode=2009Sci...324..265A}}</ref> ''[[Trichomonas vaginalis]]'',<ref name="pmid18663385">{{cite journal |vauthors=Malik SB, Pightling AW, Stefaniak LM, Schurko AM, Logsdon JM |title=An expanded inventory of conserved meiotic genes provides evidence for sex in Trichomonas vaginalis |journal=PLOS ONE |volume=3 |issue=8 |pages=e2879 |year=2008 |pmid=18663385 |pmc=2488364 |doi=10.1371/journal.pone.0002879 |bibcode=2008PLoSO...3.2879M |doi-access=free}}</ref> and [[acanthamoeba]].<ref name="pmid25800982">{{cite journal |vauthors=Khan NA, Siddiqui R |title=Is there evidence of sexual reproduction (meiosis) in Acanthamoeba? |journal=Pathog Glob Health |volume=109 |issue=4 |pages=193–5 |year=2015 |pmid=25800982 |doi=10.1179/2047773215Y.0000000009 |pmc=4530557}}</ref>

Protists generally reproduce asexually under favorable environmental conditions, but tend to reproduce sexually under stressful conditions, such as starvation or heat shock.{{Citation needed|date=December 2019|reason=removed citation to predatory publisher content}}

===Viruses===

Both animal viruses and bacterial viruses ([[bacteriophage]]) are able to undergo mating.  When a cell is mixedly infected by two genetically marked viruses, recombinant virus progeny are often observed indicating that mating interaction had occurred at the DNA level.  Another manifestation of mating between viral genomes is multiplicity reactivation (MR).  MR is the process by which at least two virus genomes, each containing inactivating genome damage, interact with each other in an infected cell to form viable progeny viruses.  The genes required for MR in bacteriophage T4 are largely the same as the genes required for allelic recombination.<ref name="pmid6261109">{{cite journal |vauthors=Bernstein C |title=Deoxyribonucleic acid repair in bacteriophage |journal=Microbiol. Rev. |volume=45 |issue=1 |pages=72–98 |year=1981 |pmid=6261109 |pmc=281499 |doi= 10.1128/MMBR.45.1.72-98.1981}}</ref> Examples of MR in animal viruses are described in the articles ''[[Herpes simplex virus]]'', ''[[Influenza A virus]]'', ''[[Adenoviridae]]'', ''[[Simian virus 40]]'', ''[[Vaccinia virus]]'', and ''[[Reoviridae]]''.