Non-helical models of DNA structure the top of this article, or there could be an equal number of right-handed and left-handed twists, as in the Rodley structure below. The abbreviation "TN", to be used to refer to any DNA structure whose strands are topologically non-linked, has been proposed. The double-helix model of DNA structure was first published in the journal "Nature" by James D. Watson and Francis Crick in 1953 with further details in 1954.) Their work was based upon the crucial X-ray diffraction image of DNA - labeled as "Photo 51" - from Rosalind Franklin in 1952, followed by her more highly clarified DNA
Molecular models of DNA is carried by spool-like proteins named histones, around which DNA winds. It is the further compaction of this DNA-protein complex which produces the well known mitotic eukaryotic chromosomes. In the late 1970s, alternate non-helical models of DNA structure were briefly considered as a potential solution to problems in DNA replication in plasmids and chromatin. However, the models were set aside in favor of the double-helical model due to subsequent experimental advances such as X-ray crystallography of DNA duplexes, and later the nucleosome core particle, and the discovery of topoisomerases. Such non-double-helical models are not currently accepted by the mainstream scientific