hot XXXXXXXXXX action

http://www.newscientist.com/news/news.jsp?id=ns99996568

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 ten-chromosome chains that determine their sex.