The mutation spectrum at the lacI gene in macrophages, follicular B cells, and GC B cells from WT and Msh2^−/− mice. (A) The mutation spectrum in the indicated cell types and genotypes showing the original nucleotide (left) and the mutation (top). Most of the mutations in macrophages and follicular B cells are G:C to A:T transition mutations, whereas in GC B cells, there is a high proportion of mutations at A:T base pairs. (B) The percentage of G:C and A:T mutations are plotted for the indicated cell types and genotypes. This figure was plotted from the data shown in panel A. Statistical analysis was carried out with a 2-tailed t test.