The ZW sex-determination system is a system that birds, some fishes, and some insects (including butterflies and moths) use to determine the sex of their offspring. The ovum is what decides the sex of the offspring in this system, in contrast to the XY sex-determination system and the X0 sex-determination system. The reason for the letters Z and W is so that this system's sex chromosomes are not confused with the X and Y sex chromosomes. Males are the homogametic sex (ZZ), while females are heterogametic (ZW).

See also

• X chromosome
• Y chromosome
• chromosome
• sexual differentiation
• Sex-determination system
  • XY sex-determination system
  • X0 sex-determination system
  • Haplo-diploid sex-determination system

Sex-determination systems