Besides the XY system are there other sex determination systems?
Some animals have a sex determination system dissimilar from the XY system.
The X0 system is the sex determination system of many insects; in this system the females are XX and the males have only one X chromosome (a conditioned shown by X0).
In birds, in some fishes and in lepidopterae (butterflies) insects the sex determination is made by the ZW system; in this system females are ZW and males are ZZ.