Some animals have a determination
system different from XY system.
The X0 is the sex determination
of many insects; in system
the females are and the males have
one X chromosome (a
represented by X0).

In , in some fish and
lepidopterae (butterflies) insects the
determination is made by ZW
system; in this females are ZW
and are ZZ.

In another , the haploid-diploid
sex determination , one of the
sexes represented by the fertilized
individual and the individual
the opposite sex is by
parthenogenesis, being haploid (
occurs in bees and insects).