George Gershwin’s magnificent Porgy and Bess, opening this weekend at Court Theatre, has such a large and thorny history, Court’s mounted a companion exhibit to explain it all. But don’t look for it at the theater: “The History of an American Symbol: Porgy and Bess” is running in the lobby gallery on the lower level of the DuSable Museum. There’s also a free discussion at DuSable, at 4:00 PM Sunday, May 22, featuring director Charles Newell and University of Chicago ethnomusicologist Travis Jackson, moderated by DuSable’s Jomo Cheatham.