Also alot of animals are hermafrodites - Some can literally split down the middle and become two identical individuals, others can regenerate most of their body if they are split in half- or even more pieces because they have stemcells spread around on their body. Another version can create whole colonies of individuals that are linked (similar to splitting into 2, however they stay connected). Others can have sex with themselves, if no compatible mate is around.
applesdontpee, There are many different methods used for sex determination. X/Y is just one. Some animals don't use genes at all. Humans (like many animals) use genes and chemicals (with interesting results when the two don't agree. Hormones tend to win)
Not all animals have gender based on the x and y chromosome system humans have. This is due to divergent evolution. Many animals by default have female offspring and it's the presence of something that causes male. For example many amphibians and reptiles have gender based on temperature. If the eggs reach a certain temperature in the nest then they become male, otherwise they are female. In hymenoptera (bees, wasps, ants, etc), though, the default is male and fertilization leads to females. Females have 2 different chromosomes while males have only 1 single chromosome. Birds have an entirely different system too.
Sorry for the long post, I'm a genetics student and that caught my eye!
18 M
One could think the ants has being hermaphrodite; the "males" being a reproductor organ, and "their" sperm being Queen's.