Did you know that alligators and crocodiles have no sex chromosomes? These would be the chromosomes that determine male or female. Instead, they exhibit something called temperature dependent sex determination (TSD, scientists love their acronyms) where if the egg is incubated at a certain temperature, then it's a male, and if it's another temperature, then the eggs become female. The difference is usually only 1-2 degrees C, and if the incubation temperature is borderline, then there is a mix of both genders.
Weird but true. That's why I love biology.