A form of DNA in which four oligo(G) sequences, either of the same or of different strands, line up either in a parallel, an anti-parallel or in a fold-back (mixed parallel and antiparallel) pattern. The interior of quadruple the helix has four guanine bases in Hoogstein base pairings; each plane of four guanines is separated from the adjacent plane by a Na⁺ or K⁺ ion. Although these structures have not been identified cells, they are strongly suspected to cap the ends of chromosomal DNA. see telomere