Researchers have discovered that a protein, called Chd5, plays an important role in male fertility. On the left is a sperm cell from a mouse that has two normal copies of the Chd5 gene. The sperm is healthy and the mouse is fertile. In the absence of Chd5, mice are infertile and their sperm cells are misshapen (three examples on the right). The researchers discovered that loss of Chd5 disrupts DNA packaging which causes infertility.