When, in a nucleic acid sequence, the four letters C, G, A, T (or U) are replaced by suitable graphical symbols, some patterns become immediately apparent. Two sets of symbols, constructed for the analysis of either purine/pyrimidine alternations, or of regions of complementarity within a sequence are shown. In addition, another mode of coding is presented, in which the four letters are represented by vectors. The sequence is thus transformed into a planar trajectory. We show, in the case of the gene for human beta hemoglobin, that such a coding enables an easy discrimination between introns and exons.