DNA is the nucleic acid that forms the genetic material in all organisms. The structure of deoxyribose nucleic acid was elucidated by Watson and Crick. The DNA is a double helical structure having two anti-parallel strands of polynucleotide chains joined to each other by hydrogen bonding formed between the N-bases. The typical DNA length is approximately $2.2$ m and the nuclei size is approximately ${10}^{-6}\mathrm{ }\mathrm{m}$ . To accommodate such a large molecule in such a tiny space, DNA undergoes a series of folding and packaging process.

DNA is wrapped with histone proteins to form beads like a structure called nucleosomes. This structure is further condensed to fit in a coiled helical structure called a solenoid. Further super folding of solenoid results in chromatin fiber formation and later into a chromatid visible during the prophase of cell division. At the metaphase of cell division, chromosome structure forms with chromatids joined at the centre by centromere.