Editing Sex-determination system (section)

===Other chromosomal systems===
In systems with two sex chromosomes, they can be heteromorphic or homomorphic. Homomorphic sex chromosomes are almost identical in size and gene content. The two familiar kinds of sex chromosome pairs (XY and ZW) are heteromorphic. Homomorphic sex chromosomes exist among pufferfish, ratite birds, pythons, and European tree frogs. Some are quite old, meaning that there is some evolutionary force that resists their differentiation.<ref name="Wright-2016">{{Cite journal |last1=Wright |first1=Alison E. |last2=Dean |first2=Rebecca |last3=Zimmer |first3=Fabian |last4=Mank |first4=Judith E. |date=2016-07-04 |title=How to make a sex chromosome |journal=Nature Communications |volume=7 |issue=1 |pages=12087 |doi=10.1038/ncomms12087 |pmid=27373494 |pmc=4932193 |bibcode=2016NatCo...712087W |issn=2041-1723}}</ref> For example, three species of [[European tree frogs]] have homologous, homomorphic sex chromosomes, and this homomorphism was maintained for at least 5.4 million years by occasional recombination.<ref>{{Cite journal |last1=Stöck |first1=Matthias |last2=Horn |first2=Agnès |last3=Grossen |first3=Christine |last4=Lindtke |first4=Dorothea |last5=Sermier |first5=Roberto |last6=Betto-Colliard |first6=Caroline |last7=Dufresnes |first7=Christophe |last8=Bonjour |first8=Emmanuel |last9=Dumas |first9=Zoé |last10=Luquet |first10=Emilien |last11=Maddalena |first11=Tiziano |last12=Sousa |first12=Helena Clavero |last13=Martinez-Solano |first13=Iñigo |last14=Perrin |first14=Nicolas |date=2011-05-17 |editor-last=Rice |editor-first=William R. |title=Ever-Young Sex Chromosomes in European Tree Frogs |journal=PLOS Biology |volume=9 |issue=5 |pages=e1001062 |doi=10.1371/journal.pbio.1001062 |doi-access=free |issn=1545-7885 |pmc=3100596 |pmid=21629756}}</ref>

The ''[[Nematocera]]'', particularly the ''[[Black fly|Simuliids]]'' and [[Chironomidae|''Chironomus'']], have sex determination regions that are labile, meaning that one species may have the sex determination region in one chromosome, but a closely related species might have the same region moved to a different non-[[Sequence homology|homologous chromosome]]. Some species even have the sex determination region different among individuals ''within'' ''the same species'' ([[intraspecific variation]]).<ref>{{Cite journal |last1=Furman |first1=Benjamin L S |last2=Metzger |first2=David C H |last3=Darolti |first3=Iulia |last4=Wright |first4=Alison E |last5=Sandkam |first5=Benjamin A |last6=Almeida |first6=Pedro |last7=Shu |first7=Jacelyn J |last8=Mank |first8=Judith E |date=2020-06-01 |editor-last=Fraser |editor-first=Bonnie |title=Sex Chromosome Evolution: So Many Exceptions to the Rules |url=https://academic.oup.com/gbe/article/12/6/750/5823304 |journal=Genome Biology and Evolution |volume=12 |issue=6 |pages=750–763 |doi=10.1093/gbe/evaa081 |issn=1759-6653 |pmc=7268786 |pmid=32315410}}</ref><ref>{{Cite journal |last1=Martin |first1=Jon |last2=Lee |first2=B. T. O. |date=September 1984 |title=A phylogenetic study of sex determiner location in a group of Australasian Chironomus species (Diptera, Chironomidae) |url=http://link.springer.com/10.1007/BF00292396 |journal=Chromosoma |volume=90 |issue=3 |pages=190–197 |doi=10.1007/BF00292396 |issn=0009-5915}}</ref><ref>{{Cite journal |last1=Martin |first1=Jon |last2=Kuvangkadilok |first2=Chaliow |last3=Peart |first3=Dianne H. |last4=Lee |first4=Barry T. O. |date=June 1980 |title=Multiple sex determining regions in a group of related Chironomus species (Diptera:Chironomidae) |url=https://www.nature.com/articles/hdy198034 |journal=Heredity |volume=44 |issue=3 |pages=367–382 |doi=10.1038/hdy.1980.34 |issn=1365-2540}}</ref> In some species, some populations have homomorphic sex chromosomes while other populations have heteromorphic sex chromosomes.

The New Zealand frog, ''[[Hochstetter's frog|Leiopelma hochstetteri]]'', uses a [[B chromosome|supernumerary sex chromosome]]. With zero of that chromosome, the frog develops into a male. With one or more, the frog develops into a female. One female had as many as 16 of that chromosome.<ref>{{Cite journal |last=Green |first=David M. |date=1988-09-01 |title=Cytogenetics of the endemic New Zealand frog, Leiopelma hochstetteri: extraordinary supernumerary chromosome variation and a unique sex-chromosome system |url=https://doi.org/10.1007/BF00331795 |journal=Chromosoma |volume=97 |issue=1 |pages=55–70 |doi=10.1007/BF00331795 |issn=1432-0886}}</ref>

Different populations of the [[Japanese wrinkled frog|Japanese frog ''Rana rugosa'']] uses different systems. Two use homomorphic male heterogamety, one uses XX/XY, one uses ZZ/ZW. Remarkably, the X and Z chromosomes are homologous, and the Y and W as well. ''Dmrt1'' is on autosome 1 and not sex-linked. This means that an XX female individual is genetically similar to a ZZ male individual, and an XY male individual is to a ZW female individual. The mechanism behind this is yet unclear, but it is hypothesized that during its recent evolution, the XY-to-ZW transition occurred twice.<ref>{{Cite journal |last1=Uno |first1=Yoshinobu |last2=Nishida |first2=Chizuko |last3=Oshima |first3=Yuki |last4=Yokoyama |first4=Satoshi |last5=Miura |first5=Ikuo |last6=Matsuda |first6=Yoichi |last7=Nakamura |first7=Masahisa |date=June 2008 |title=Comparative chromosome mapping of sex-linked genes and identification of sex chromosomal rearrangements in the Japanese wrinkled frog (Rana rugosa, Ranidae) with ZW and XY sex chromosome systems |url=https://link.springer.com/10.1007/s10577-008-1217-7 |journal=Chromosome Research |volume=16 |issue=4 |pages=637–647 |doi=10.1007/s10577-008-1217-7 |pmid=18484182 |issn=0967-3849}}</ref><ref name="Graves-2008">{{Cite journal |last=Graves |first=Jennifer A. Marshall |date=2008-12-01 |title=Weird Animal Genomes and the Evolution of Vertebrate Sex and Sex Chromosomes |url=http://dx.doi.org/10.1146/annurev.genet.42.110807.091714 |journal=Annual Review of Genetics |volume=42 |issue=1 |pages=565–586 |doi=10.1146/annurev.genet.42.110807.091714 |issn=0066-4197}}</ref>

''[[Clarias gariepinus]]'' uses both XX/XY and ZW/ZZ system within the species, with some populations using homomorphic XX/XY while others using heteromorphic ZW/ZZ. A population in Thailand appears to use both systems simultaneously, possibly because ''C. gariepinus'' were not native to Thailand, and were introduced from different source populations which resulted in a mixture.<ref>{{Cite journal |last1=Nguyen |first1=Dung Ho My |last2=Panthum |first2=Thitipong |last3=Ponjarat |first3=Jatupong |last4=Laopichienpong |first4=Nararat |last5=Kraichak |first5=Ekaphan |last6=Singchat |first6=Worapong |last7=Ahmad |first7=Syed Farhan |last8=Muangmai |first8=Narongrit |last9=Peyachoknagul |first9=Surin |last10=Na-Nakorn |first10=Uthairat |last11=Srikulnath |first11=Kornsorn |date=2021-01-05 |title=An Investigation of ZZ/ZW and XX/XY Sex Determination Systems in North African Catfish (Clarias gariepinus, Burchell, 1822) |journal=Frontiers in Genetics |volume=11 |doi=10.3389/fgene.2020.562856 |doi-access=free |pmid=33584785 |issn=1664-8021|pmc=7874028 }}</ref>

Multiple sex chromosomes like those of platypus also occurs in bony fish.<ref>{{Cite journal |last1=Sember |first1=Alexandr |last2=Nguyen |first2=Petr |last3=Perez |first3=Manolo F. |last4=Altmanová |first4=Marie |last5=Ráb |first5=Petr |last6=Cioffi |first6=Marcelo de Bello |date=2021-09-13 |title=Multiple sex chromosomes in teleost fishes from a cytogenetic perspective: state of the art and future challenges |journal=Philosophical Transactions of the Royal Society B: Biological Sciences |volume=376 |issue=1833 |pages=20200098 |doi=10.1098/rstb.2020.0098 |issn=0962-8436 |pmc=8310710 |pmid=34304595}}</ref> Some moths and butterflies have <math>W_1W_2Z \text {♀}/ZZ \text{♂}</math> or <math>WZ_1Z_2 \text {♀}/Z_1Z_1Z_2Z_2 \text{♂}</math>.<ref>{{Cite journal |last1=Traut |first1=W. |last2=Sahara |first2=K. |last3=Marec |first3=F. |date=2008-01-18 |title=Sex Chromosomes and Sex Determination in Lepidoptera |url=https://doi.org/10.1159/000111765 |journal=Sexual Development |volume=1 |issue=6 |pages=332–346 |doi=10.1159/000111765 |pmid=18391545 |issn=1661-5425}}</ref>

The [[Southern platyfish#Sex|Southern platyfish]] has a complex sex determination system involving 3 sex chromosomes and 4 autosomal alleles.<ref>{{Citation |last=Kallman |first=Klaus D. |title=A New Look at Sex Determination in Poeciliid Fishes |date=1984 |work=Evolutionary Genetics of Fishes |pages=95–171 |editor-last=Turner |editor-first=Bruce J. |url=https://doi.org/10.1007/978-1-4684-4652-4_3 |access-date=2024-08-04 |place=Boston, MA |publisher=Springer US |doi=10.1007/978-1-4684-4652-4_3 |isbn=978-1-4684-4652-4}}</ref><ref name="Schartl-2004b">{{cite journal |vauthors=Schartl M |date=July 2004 |title=A comparative view on sex determination in medaka |journal=Mechanisms of Development |volume=121 |issue=7–8 |pages=639–645 |doi=10.1016/j.mod.2004.03.001 |pmid=15210173 |s2cid=17401686 |doi-access=free}}</ref>

''[[Gastrotheca pseustes]]'' has <math>XY_b \text {♀} / XY_a \text{♂}</math> [[Karyotype|C-banding]] heteromorphism, meaning that both males and females have XY chromosomes, but their Y chromosomes are different on one or more C-bands. ''[[Strabomantis biporcatus|Eleutherodactylus maussi]]'' has a <math>\mathrm{X}_1 \mathrm{X}_1 \mathrm{X}_2 \mathrm{X}_2 \text {♀} / \mathrm{X}_1 \mathrm{X}_2 \mathrm{Y} \text{♂}</math> system.<ref>{{Cite journal |last1=Schmid |first1=M. |last2=Steinlein |first2=C. |last3=Feichtinger |first3=W. |date=March 1992 |title=Chromosome banding in amphibia: XVII. First demonstration of multiple sex chromosomes in amphibians: Eleutherodactylus maussi (Anura, Leptodactylidae) |url=http://link.springer.com/10.1007/BF00346007 |journal=Chromosoma |volume=101 |issue=5–6 |pages=284–292 |doi=10.1007/BF00346007 |pmid=1576881 |issn=0009-5915}}</ref><ref>{{Cite journal |last1=Schmid |first1=M. |last2=Feichtinger |first2=W. |last3=Steinlein |first3=C. |last4=Haaf |first4=T. |last5=Schartl |first5=M. |last6=Visbal García |first6=R. |last7=Manzanilla Pupo |first7=J. |last8=Fernández Badillo |first8=A. |date=2003-08-14 |title=Chromosome banding in Amphibia: XXVI. Coexistence of homomorphic XY sex chromosomes and a derived Y-autosome translocation in Eleutherodactylus maussi (Anura, Leptodactylidae) |url=https://doi.org/10.1159/000071612 |journal=Cytogenetics and Cell Genetics |volume=99 |issue=1–4 |pages=330–343 |doi=10.1159/000071612 |pmid=12900583 |issn=0301-0171}}</ref>