Wallaby, South Stradbroke Island, Australia

A wallaby on South Stradbroke Island in Australia. Scientists long have suspected that the sex chromosome that only males carry, the Y chromosome, is deteriorating, but until now, no one has understood the evolutionary processes that control this chromosome's demise. Now, a pair of Penn State scientists, including a National Science Foundation graduate research fellow, has discovered that the Y chromosome is evolving at a rapid rate, resulting in a dramatic loss of genes that eventually could lead to the chromosome's complete disappearance. Credit: Anton Nekrutenko, Penn State University