Th e patterns of recognition elements in the major groove are unique for each of the four base pairs (G-C, C-G, A-T, and T-A). In the minor groove, however, the pattern for G-C is indistinguishable from that for C-G, and the pattern for A-T is the same as that for T-A. Th us, the major groove of DNA allows each of the four kinds of base pairs to be distinguished from each other, whereas the interactions in the minor groove do not.