Brown arrows indicate dyad axes, and arrowheads on strands indicate 3' ends. The second character of the name indicates antiparallel (DAE and DAO), with dyad axes perpendicular to the plane of the helix axes, or parallel (DPE, DPON, DPOW), with the dyad axis coplanar with the helix axes. The third character indicates whether there is an even (DAE or DPE) number of half-turns between crossovers, or an odd number (DAO, DPON, DPOW). Odd parallel molecules are further differentiated by a fourth character, N or W, indicating whether the extra half turn is a minor (N -- narrow) groove separation or a major (W -- wide) groove separation.