One out of eight couples has trouble conceiving, with a quarter of those cases caused by unexplained male infertility. Research has linked that to defective sperm that fail to ‘evict’ proteins called histones from DNA during development. However, the mechanisms behind that eviction and where this is happening has remained unclear. Now, researchers show, using newer genome-wide DNA sequencing tools, the precise genetic locations of those retained histones, and a key gene regulating it.