As humans, our sex is dictated by the combination of our sex chromosomes. XX for females and XY for Males. But other species don’t use X or Y chromosomes and some lack chromosomes completely!

Early reptiles such as the crocodile are one such species. They have no sex chromosomes and therefore their sex is regulated via the environment. On warmer days (temperatures above 32oc) developing crocodiles will follow the male developmental pathway and on cooler days (temperatures bellow 32oc) they will follow a female developmental pathway. When I first found this out I couldn’t believe it because I thought all sex was determined by genetics but it turns out it isn’t the case for all animals.

So, sex can be determined by either genetics or the environment but can both play a role? The answer is yes! Pogona viticeps can switch between both temperature and genetic determination! Furthermore Pogona doesn’t use X and Y but Z and W chromosomes!