Research shows a genetic ‘master switch’ determines sex in most animals

In humans and other animals, sex is usually determined by a single gene. However, there are claims that in some species, such as platyfish, it takes a whole “parliament” of genes acting together to determine whether offspring develop as a male or female.

In a new analysis, we took a close look at these claims. We found they describe abnormal situations, such as hybrids between two species with different sex-determining systems, or when one sex system is in the process of replacing another.

We conclude that sex is normally determined by a single gene. Evolutionary theory suggests this is the most stable state of affairs, as it ensures a 1:1 ratio of male and female animals.