We also compared the expression of several key circadian genes including Arntl, Clock, Cry1, Cry2, Per1, Per2, Per3, Nr1d1, and Npas2 in colon samples collected at 03, 09, 15, and 21 of normal mice, colitis mice, normal mice receiving BBR, and colitis mice receiving BBR. The gene discussed is PER2; the disease is colitis.