DNA, the blueprint of life, is organized into structures called chromosomes. Inprokaryotic cells, chromosomes are circular, whereas in eukaryotic cells, they are linear strands. Different organisms have different numbers of chromosomes: human cells usually have 46 chromosomes, dogs have 78 chromosomes, while kangaroos have only 12 chromosomes! When you add all these chromosomes up, each cell actually contains about 2m of DNA! And all this DNA has to fit into a tiny nucleus of 5-10um in diameter. This is like trying to stuff a piece of string 2km long (it will take you about 20 minutes to walk from one end to the other) into a tiny bead smaller than 1cm!!! To do this seemingly impossible feat, cells devised an ingenious packaging system: it wraps DNA around proteins called histones. The resulting DNA-protein complex is called chromatin.