In the Creatures games there are two genders or sexes, male and female, with different physical and genetic characteristics. For example, female creatures lay eggs, while male creatures can't, and the genders often have separate sprite variants.
Via the use of a genetic editor it is possible to give creatures of one gender the genes of the other (see Harry). It isn't possible for these norns to get pregnant or reproduce under normal circumstances due to the way the games are scripted, although third-party COBs can be used in order to initiate an artificial pregnancy.
Through some external programs (such as the Genetics Kit) or third-party agents (such as the Tombstone Creator reviving a dead mother's unborn offspring), it is possible for a creature to be born genderless in C3/DS. These creatures lack all sex-linked genes and can kisspop with both male and female creatures. The Nornbinary Update allows for genderless creatures to occur naturally and fixes UI-related glitches.