THE weird and wonderful duck-billed platypus just got weirder and more wonderful.
These milk-producing mammals lay eggs, have a bird-like bill and a skeleton with some reptilian features. Now it turns out that their sex is determined in a unique way. In most mammals, including humans, sex is decided by the X and Y chromosomes. Two Xs and you are female; XY and you’re a male. In birds the system is similar: ZW for a female and ZZ for a male.
But in the platypus, X1X1X2X2X3X3X4X…
