Barton Childs, the Johns Hopkins University professor who helped found the field of pediatric genetics, has died, reports the New York Times. He was 93. In the 1960s, Childs confirmed the Lyon hypothesis in humans. Based on mouse studies that hypothesis said that, in females' cells, one of their two X chromosomes is inactive and which one it is that is inactive occurs randomly. This, the Times adds, helped explain why women were less affected by certain genetic diseases.