A team of scientists from Australia and the United Kingdom has finally elucidated the strange sex chromosome system of the duck-billed platypus. The first study , the findings of which are published this week in PNAS , demonstrates that the platypus has 10 sex chromosomes, rather than the single pair usually found in mammals. Results of a second study , appearing this week in Nature , detail the way the chromosomes segregate during male meiosis to determine the sex of the zygote.

"The platypus has long been known to have an unusual multiple set of sex chromosomes," said the University of Melbourne's professor Marilyn Renfree, who was not involved in the studies. However, the use of fluorescence in situ hybridization (FISH) confirmed how the ten elements segregate. "Remarkably, the five X chromosomes go into one cell, and the five Y into another," she continued. "This results in two kinds of...