In a cluster of glowing human stem cells, one cell divides. The cell membrane is shown in purple, while DNA in the dividing nucleus is blue. The white fibers linking the nucleus are spindles, which aid in cell division.
Allen Institute for Cell Science
Russian tennis star Maria Sharapova isn't competing at the 2016 Olympics. At a March 7 press conference in Los Angeles, she told reporters she'd tested positive for meldonium, a prescription heart drug that improves blood flow. It was banned in January by the World Anti-Doping Agency.
Robyn Beck/AFP/Getty Images