section_path: Sex-determination systems/Genetic/ZW sex determination
section_name: ZW sex determination
paragraph_text: 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. 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 crustaceans.
  
  The majority of butterflies and moths also have a ZW sex-determination system. Females can have Z, ZZW, and even ZZWW.