Three cheetah brothers, named Draco, Granger and Zabini after the Harry Potter characters, have arrived at the National Zoo to help add genetic diversity to its breeding program. The new cheetahs go on public display Friday. Zoo reproduction specialist JoGayle Howard explained to WTOP that the new cheetahs are vital because their genetic line is not represented in North America. Cheetahs are both critically endangered and very difficult to breed, so the introduction of a…