Editing Southern platyfish (section)

== Sex ==
The southern platyfish has three sex chromosomes W, X, and Y, that interact with autosomal genes. This creates a highly complex sex determination system.<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 |language=en |doi=10.1007/978-1-4684-4652-4_3 |isbn=978-1-4684-4652-4|url-access=subscription }}</ref><ref name="Schartl">{{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>

* The Y chromosome carries a dominant male-determining gene (''M''), which is thought to be homologous to the mammalian  ''SRY'' gene located on the Y chromosome.
* The W chromosome carries a suppressor gene (''S'') that inhibits the activity of the male-determining gene (''M'') on the Y chromosome. This explains why WY individuals develop as females.
* The X chromosome lacks the suppressor gene (''S'') found on the W chromosome, allowing XY and YY individuals to develop as males.

There are 4 autosomal alleles that intervene in the sex determination system:

* A recessive autosomal factor ''a'', can, in its homozygous state (''aa''), activate the male-determining gene on the X chromosome. This leads to the development of XX males.
* Two recessive alleles ''b'' and ''c'', likely acting in concert, can activate the male-determining gene located on the W chromosome. This activation can result in WW, WX, and even WY individuals developing as males. The ''b'' factor appears to specifically suppress the W-linked suppressor (''S'').
* The dominant ''T'' allele interacts with a specific variant of the Y chromosome (designated as Y') to promote female development in some XY individuals.

{| class="wikitable"
|+Sex chromosome combinations in ''Xiphophorus maculatus''
!Genotype
!Sex
|-
|WW
|Female
|-
|WX
|Female
|-
|WY
|Female
|-
|XX
|Usually female, but can be male under the influence of autosomal factors
|-
|XY
|Usually Male, but can be female with the Y' chromosome and ''T'' autosomal allele.
|-
|YY
|Male
|}