Editing Sex (section)

==== ZW sex determination ====
In birds, which have a [[ZW sex-determination system]], the W chromosome carries factors responsible for female development, and default development is male.<ref>{{cite journal | vauthors = Smith CA, Katz M, Sinclair AH | title = DMRT1 is upregulated in the gonads during female-to-male sex reversal in ZW chicken embryos | journal = Biology of Reproduction | volume = 68 | issue = 2 | pages = 560–570 | date = February 2003 | pmid = 12533420 | doi = 10.1095/biolreprod.102.007294 | doi-access = free }}</ref> In this case, ZZ individuals are male and ZW are female. It is the female [[gamete]] that determines the sex of the offspring. This system is used by birds, some fish, and some [[crustacean]]s.<ref name="Hake-2008" />

The majority of [[Lepidoptera|butterflies and moths]] also have a ZW sex-determination system. Females can have Z, ZZW, and even ZZWW.<ref>{{cite book| vauthors = Majerus ME | author-link = Michael Majerus |url= {{GBurl|id=vDHOYPQ2mmYC|q=ZW+sex+determination}}|title=Sex Wars: Genes, Bacteria, and Biased Sex Ratios|date=2003|publisher=Princeton University Press|isbn=978-0-691-00981-0|page=59|language=en}}</ref>