Within minutes of fertilization, the egg of a fruit fly becomes a scene from the battle of the sexes. The egg attacks and destroys the cellular "power plants" (mitochondria) from the sperm that had fertilized it, so that only its own mitochondria remain. These findings from a new Weizmann Institute of Science study, published in Nature Communications, might provide insights into advanced fertilization treatments and shed light on a long-standing mystery: How and why do we inherit all of our mitochondria from our mothers?