In eukaryotes, the organisation of DNA is much more complex and is carried out by a set of positively charged basic protein called histones. Basic amino acid residue lysines and arginines with charged side chains are abundantly found in histones. Nucleosome is formed when the wrapping up of negatively charged DNA around the positively charged histone octamer occurs. To complete about 1¾ turns, about 200 bp of DNA is wrapped over nu-body, this forms nucleosome of size 110×60 Å. With about 80 base pairs, DNA present between two adjacent nucleosome is called linker DNA. A 'beads on string' appearance under electron microscope is given by the nucleosomes in chromatin. The nucleosome coils further to form solenoid or chromatin fibres which has a diameter of 30 nm. Chromosomes are formed by further coiling and condensation of the chromatin fibres at metaphase stage of cell division. Non-histone chromosomal proteins (NHC) are additional set of proteins that are required at higher levels for the packaging of chromatin. Therefore, the organisation of genetic material from smallest to largest is: nucleotide, DNA, gene, nucleosome, chromosome, genome.