The structures shown are named by the acronym describing their basic characteristics.
All names begin with 'D' for double crossover.
The second character refers to the relative orientations of their two double helical domains, 'A' for antiparallel and 'P' for parallel. A fourth character is needed to describe parallel double crossover molecules with an odd number of helical half-turns between crossovers. The strands are drawn as zig-zag helical structures, where two consecutive, perpendicular lines correspond to a full helical turn for a strand. The arrowheads at the ends of the strands designate their 3' ends. Note that the dyad in DAE is only approximate, because the central strand contains a nick, which destroys the symmetry.