(a) Mutant frequencies and (b) independent mutation frequencies in the small intestine of Msh2-bearing (Msh2+/+) and Msh2-KO (Msh2−/−) mice carrying gpt. Potassium bromate was orally administered to the mice via the drinking water (1.5 g/L) for 28 days, or the vehicle control (Cont.). Independent mutation frequency is defined as frequency of independent mutants. Blue bars, total frequency; green bars, frequency of G-to-A transition; red bars, frequency of G-to-T transversion; yellow bars, frequency of A-to-T transversion. Data are presented as mean ± SD. * P < 0.05, ** P < 0.01, significantly different compared with Cont. of Msh2-bearing gpt delta mice. # P < 0.05, ## P < 0.01, significantly different compared with Msh2-bearing gpt delta mice administered potassium bromate.