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In humans if you have two X chromosomes you are female and if you have an X and a Y then you are male. It is textbook science. But CrowdScience listener Du in Singapore has done some extra homework and found a piece of intriguing fish research which suggests a different outcome, at least for one species – tilapia, a popular fish on restaurant menus worldwide and as it happens, the first fish to visit space. Whilst humans couldn’t exist without an X-chromosome, tilapia apparently, can. In fact, they are happy with just two Y chromosomes. The existence of this odd breed comes down to the tilapia fish’s ability to change from male to female.

Nature has come up with an array of bizarre solutions when it comes to sex determination and what sets you on one genetic path or another. And like with the tilapia fish, the decision isn't always for life. Some species of fish, lizards and even birds sidestep the chromosome system and morph between the sexes to survive a changing environment. How can they have both genetic sex pathways latent within them? And why can’t humans do the same trick?

Presenter: Marnie Chesterton

Producer: Louisa Field

(Photo: A male Asian sheepshead wrasse courting a female featured in Â鶹ԼÅÄ’s Blue Planet II. Credit: Getty Images)