ambiguity characters have been selected from the remaining characters of the Roman alphabet. The authors of the notation endeavored to select ambiguity characters with logical mnemonics. For example, S is used to represent the possibility of finding cytosine or guanine at genetic loci, both of which form strong cross-strand binding interactions. Conversely, the weaker interactions of thymine and adenine are represented by a W. However, convenient mnemonics are not as readily available for the other ambiguity characters displayed in Table 1. This has made ambiguity characters difficult to use and may account for their limited application. Nucleic acid nomenclature The positions of the carbons in the ribose sugar that forms the backbone of the nucleic acid chain are numbered, and are used to indicate the direction of nucleic acids (5'->3' versus 3'->5'). This is referred to as directionality. Alternative visually enhanced notations Legibility issues associated with IUPAC-encoded genetic data have led biologists to consider alternative strategies for displaying genetic data. These creative approaches to visualizing DNA sequences have generally relied on the use of spatially distributed symbols and/or visually distinct shapes to encode lengthy nucleic acid sequences. Alternative notations for nucleotide sequences have been attempted, however general uptake has been low. Several of these approaches are summarized below. Stave projection In 1986, Cowin et al. described a novel method for visualizing DNA sequence known as the Stave Projection. Their strategy was to encode nucleotides as circles on series of horizontal bars akin to notes on musical stave. As illustrated in Figure 1, each gap on the five-line staff corresponded to one of the four DNA bases. The spatial distribution of the circles made it far easier to distinguish individual bases and compare genetic sequences than IUPAC-encoded data. The order of the bases (from top to bottom, G, A, T, C) is chosen so that the complementary strand can be read by turning the projection upside down. Geometric symbols Zimmerman et al. took a different approach to visualizing genetic data. Rather than relying on spatially distributed circles to highlight genetic features, they exploited four geometrically diverse symbols found in a standard computer font to distinguish the four bases. The authors developed a simple WordPerfect macro to translate IUPAC characters into the more visually distinct symbols. DNA Skyline With the growing availability of font editors, Jarvius and Landegren devised a novel set of genetic symbols, known as the DNA Skyline font, which