Platypus Trivia

In most mammals, including humans, sex is decided by the X and Y chromosomes: two Xs create a female, while XY creates a male. In birds, the system is similar: ZW makes for a female, while ZZ makes for a male.

But in platypuses, XXXXXXXXXX creates a female, while XYXYXYXYXY creates a male. In other words, rather than a single chromosome pair, platypuses have a set of ten-chromosomes that determine their sex.

(NewScientist: “Platypus sex is XXXXX-rated,” by Rachel Nowak [October 24, 2004])