Editing XY sex-determination system (section)

== Mechanisms ==
All [[animal]]s have a set of [[DNA]] coding for [[gene]]s present on [[chromosome]]s. In humans, most mammals, and some other species, two of the [[chromosome]]s, called the [[X chromosome]] and [[Y chromosome]], code for sex. In these species, one or more [[gene]]s are present on their [[Y chromosome]] that determine maleness. In this process, an [[X chromosome]] and a [[Y chromosome]] act to determine the sex of offspring, often due to genes located on the Y chromosome that code for maleness. Offspring have two sex chromosomes: an offspring with two X chromosomes (XX) will develop female characteristics, and an offspring with an X and a Y chromosome (XY) will develop male characteristics, except in various exceptions such as individuals with [[XY gonadal dysgenesis|Swyer syndrome]], that have XY chromosomes and a female phenotype, and [[XX male syndrome|de la Chapelle Syndrome]], that have XX chromosomes and a male phenotype, however these exceptions are rare.

=== Mammals ===
In most mammals, sex is determined by presence of the Y chromosome. This makes individuals with [[Klinefelter syndrome|XXY]] and [[XYY syndrome|XYY]] karyotypes males, and individuals with [[Turner syndrome|X]] and [[Trisomy X|XXX]] karyotypes females.<ref name="Hake-2014" />

In the 1930s, [[Alfred Jost]] determined that the presence of [[testosterone]] was required for [[Wolffian duct]] development in the male rabbit.<ref name="Jost-1970">{{cite journal | vauthors = Jost A | title = Hormonal factors in the sex differentiation of the mammalian foetus | journal = Philosophical Transactions of the Royal Society of London. Series B, Biological Sciences | volume = 259 | issue = 828 | pages = 119–130 | date = August 1970 | pmid = 4399057 | doi = 10.1098/rstb.1970.0052 | bibcode = 1970RSPTB.259..119J | doi-access = free | jstor = 2417046 }}</ref>

SRY is a sex-determining gene on the Y chromosome in the [[theria]]ns (placental mammals and marsupials).<ref name="Wallis-2008">{{cite journal | vauthors = Wallis MC, Waters PD, Graves JA | title = Sex determination in mammals--before and after the evolution of SRY | journal = Cellular and Molecular Life Sciences | volume = 65 | issue = 20 | pages = 3182–3195 | date = October 2008 | pmid = 18581056 | pmc = 11131626 | doi = 10.1007/s00018-008-8109-z | s2cid = 31675679 }}</ref> Non-human mammals use several genes on the Y chromosome.{{Citation needed|date=August 2021|reason=Your explanation here}}

Not all male-specific genes are located on the [[Y chromosome]]. The [[platypus]], a [[monotreme]], use five pairs of different XY chromosomes with six groups of male-linked genes, [[Anti-Müllerian hormone|AMH]] being the master switch.<ref>{{cite journal | vauthors = Cortez D, Marin R, Toledo-Flores D, Froidevaux L, Liechti A, Waters PD, Grützner F, Kaessmann H | title = Origins and functional evolution of Y chromosomes across mammals | journal = Nature | volume = 508 | issue = 7497 | pages = 488–493 | date = April 2014 | pmid = 24759410 | doi = 10.1038/nature13151 | url = https://odin.mdacc.tmc.edu/~ryu/materials/papers/nature2014April_EvolutionYChrom.pdf | url-status = live | bibcode = 2014Natur.508..488C | s2cid = 4462870 | s2cid-access = free | archive-url = https://web.archive.org/web/20170810203303/http://odin.mdacc.tmc.edu/~ryu/materials/papers/nature2014April_EvolutionYChrom.pdf | archive-date = Aug 10, 2017 }}</ref>

====Humans====
[[File:Human male karyotpe high resolution - XY chromosome cropped.JPG|thumb|199px|Human male XY chromosomes after [[G-banding]]]]
A single gene (''[[SRY]]'') present on the Y chromosome acts as a signal to set the developmental pathway towards maleness. Presence of this gene starts off the process of [[virilization]]. This and other factors result in the [[sex differences in humans]].<ref name="Fauci-2008">{{Cite book|title = Harrison's Principles of Internal Medicine|url = https://archive.org/details/harrisonsprincip00asfa|url-access = limited| vauthors = Fauci AS, Braunwald E, Kasper DL, Hauser SL, Longo DL, Jameson JL, Loscalzo J |publisher = McGraw-Hill Medical|year = 2008|isbn = 978-0-07-147693-5|pages = [https://archive.org/details/harrisonsprincip00asfa/page/n2377 2339]–2346 |edition = 17th }}</ref> The cells in females, with two X chromosomes, undergo [[X-inactivation]], in which one of the two X chromosomes is inactivated. The inactivated X chromosome remains within a cell as a [[Barr body]].

===Other animals===
Some species of [[turtle]]s have convergently evolved XY sex determination systems, specifically those in [[Chelidae]] and [[Staurotypinae]].<ref>{{cite journal | vauthors = Badenhorst D, Stanyon R, Engstrom T, Valenzuela N | title = A ZZ/ZW microchromosome system in the spiny softshell turtle, Apalone spinifera, reveals an intriguing sex chromosome conservation in Trionychidae | journal = Chromosome Research | volume = 21 | issue = 2 | pages = 137–147 | date = April 2013 | pmid = 23512312 | doi = 10.1007/s10577-013-9343-2 | s2cid = 14434440 }}</ref>

Other species (including most ''[[Drosophila]]'' species) use the presence of two X chromosomes to determine femaleness: one X chromosome gives putative maleness, but the presence of Y chromosome genes is required for normal male development. In the fruit fly individuals with XY are male and individuals with XX are female; however, individuals with XXY or XXX can also be female, and individuals with X can be males.<ref>{{Cite book|url=https://books.google.com/books?id=AKGsDwAAQBAJ|title=The Biology of Reproduction|vauthors=Fusco G, Minelli A|date=2019-10-10|publisher=Cambridge University Press|isbn=978-1-108-49985-9|pages=306–308|author-link2=Alessandro Minelli (biologist)}}</ref>

=== Plants ===

==== Angiosperms ====
While very few species of [[Dioecy|dioecious]] [[Flowering plant|angiosperm]] have XY sex determination, making up less than 5% of all species, the sheer diversity of angiosperms means that the total number of species with XY sex determination is actually quite high, estimated to be at around 13,000 species. Molecular and evolutionary studies also show that XY sex determination has evolved independently many times in upwards of 175 unique families, with a recent study suggesting its evolution has independently occurred hundreds to thousands of times.<ref>{{Cite journal |last1=Leite Montalvão |first1=Ana Paula |last2=Kersten |first2=Birgit |last3=Fladung |first3=Matthias |last4=Müller |first4=Niels Andreas |date=2021-01-15 |title=The Diversity and Dynamics of Sex Determination in Dioecious Plants |journal=Frontiers in Plant Science |language=English |volume=11 |doi=10.3389/fpls.2020.580488 |doi-access=free |pmid=33519840 |pmc=7843427 |issn=1664-462X}}</ref> 

Many economically important crops are known to have an XY system of sex determination, including kiwifruit,<ref>{{Cite journal |last1=Akagi |first1=Takashi |last2=Pilkington |first2=Sarah M. |last3=Varkonyi-Gasic |first3=Erika |last4=Henry |first4=Isabelle M. |last5=Sugano |first5=Shigeo S. |last6=Sonoda |first6=Minori |last7=Firl |first7=Alana |last8=McNeilage |first8=Mark A. |last9=Douglas |first9=Mikaela J. |last10=Wang |first10=Tianchi |last11=Rebstock |first11=Ria |last12=Voogd |first12=Charlotte |last13=Datson |first13=Paul |last14=Allan |first14=Andrew C. |last15=Beppu |first15=Kenji |date=August 2019 |title=Two Y-chromosome-encoded genes determine sex in kiwifruit |url=https://www.nature.com/articles/s41477-019-0489-6 |journal=Nature Plants |language=en |volume=5 |issue=8 |pages=801–809 |doi=10.1038/s41477-019-0489-6 |pmid=31383971 |bibcode=2019NatPl...5..801A |issn=2055-0278}}</ref> asparagus,<ref>{{Cite journal |last1=Harkess |first1=Alex |last2=Huang |first2=Kun |last3=van der Hulst |first3=Ron |last4=Tissen |first4=Bart |last5=Caplan |first5=Jeffrey L. |last6=Koppula |first6=Aakash |last7=Batish |first7=Mona |last8=Meyers |first8=Blake C. |last9=Leebens-Mack |first9=Jim |date=June 2020 |title=Sex Determination by Two Y-Linked Genes in Garden Asparagus |journal=The Plant Cell |volume=32 |issue=6 |pages=1790–1796 |doi=10.1105/tpc.19.00859 |issn=1532-298X |pmc=7268802 |pmid=32220850}}</ref> grapes<ref>{{Cite journal |last1=Picq |first1=Sandrine |last2=Santoni |first2=Sylvain |last3=Lacombe |first3=Thierry |last4=Latreille |first4=Muriel |last5=Weber |first5=Audrey |last6=Ardisson |first6=Morgane |last7=Ivorra |first7=Sarah |last8=Maghradze |first8=David |last9=Arroyo-Garcia |first9=Rosa |last10=Chatelet |first10=Philippe |last11=This |first11=Patrice |last12=Terral |first12=Jean-Frédéric |last13=Bacilieri |first13=Roberto |date=2014-09-03 |title=A small XY chromosomal region explains sex determination in wild dioecious V. vinifera and the reversal to hermaphroditism in domesticated grapevines |journal=BMC Plant Biology |volume=14 |issue=1 |pages=229 |doi=10.1186/s12870-014-0229-z |doi-access=free |issn=1471-2229 |pmc=4167142 |pmid=25179565}}</ref> and date palms.<ref>{{Cite journal |last1=Intha |first1=Noppharat |last2=Chaiprasart |first2=Peerasak |date=2018-06-16 |title=Sex determination in date palm (Phoenix dactylifera L.) by PCR based marker analysis |url=https://www.sciencedirect.com/science/article/abs/pii/S0304423818302073 |journal=Scientia Horticulturae |volume=236 |pages=251–255 |doi=10.1016/j.scienta.2018.03.039 |bibcode=2018ScHor.236..251I |issn=0304-4238}}</ref>

==== Gymnosperms ====
In sharp contrast to angiosperms, approximately 65% of [[Gymnosperm|gymnosperms]] are dioecious. Some families which contain members that are known to have a XY system of sex determination include the cycad families [[Cycas|Cycadaceae]] and [[Zamiaceae]], [[Ginkgoaceae]], [[Gnetum|Gnetaceae]] and [[Podocarpaceae]].<ref>{{Cite journal |last1=Ohri |first1=Deepak |last2=Rastogi |first2=Shubhi |date=2020-04-01 |title=Sex determination in gymnosperms |url=https://link.springer.com/article/10.1007/s13237-019-00297-w/tables/1 |journal=The Nucleus |language=en |volume=63 |issue=1 |pages=75–80 |doi=10.1007/s13237-019-00297-w |issn=0976-7975}}</ref>

===Other systems===
{{Main|Sex determination system}}

Whilst XY sex determination is the most familiar, since it is the system that humans use, there are a range of alternative systems found in nature. The inverse of the XY system (called ''[[ZW sex-determination system|ZW]]'' to distinguish it) is used in birds and many insects, in which it is the females that are heterogametic (ZW), while males are homogametic (ZZ).<ref>{{cite journal | vauthors = Smith CA, Sinclair AH | title = Sex determination: insights from the chicken | journal = BioEssays | volume = 26 | issue = 2 | pages = 120–132 | date = February 2004 | pmid = 14745830 | doi = 10.1002/bies.10400 | doi-access = free }}</ref> 

Many insects of the order [[Hymenoptera]] instead have a [[haplo-diploid sex-determination system|''haplo-diploid'' system]], where the females are full [[diploid|diploids]] (with all chromosomes appearing in pairs) but males are [[haploid]] (having just one copy of all chromosomes). Some other insects have the ''[[X0 sex-determination system]]'', where just the sex-determining chromosome varies in ploidy (XX in females but X in males), while all other chromosomes appear in pairs in both sexes.<ref>{{cite web | vauthors = Lee C |url=https://genetics.knoji.com/5-types-of-sex-determination-in-animals/|title=5 Types of Sex Determination in Animals| work = Knoji Consumer Knowledge |access-date=3 May 2018|url-status=live|archive-url=https://web.archive.org/web/20170205101323/https://genetics.knoji.com/5-types-of-sex-determination-in-animals/|archive-date=5 February 2017}}</ref>