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.
Did you know: If a female creature within C3/DS dies whilst she is pregnant, a glitch can sometimes occur causing the offspring to be born genderless, despite using sprites from either gender. A selection of genderless creatures can be found on The Creatures Repository here.