Chromosomes are physical carriers of genetic information that all organisms rely on as blueprints. The chromosome consists of deoxyribonucleic acid (DNA) and proteins. The DNA of the chromosome stores genetic information, with the content and the selective expression of which determining the diversity of all living organisms. Chromosomes come in different shapes. Prokaryotic organisms usually have simple circular chromosomes, whereas eukaryotic organisms such as plants and animals have developed highly organized linear chromosome structures. In eukaryotes, DNA and histone proteins are packaged into nucleosomes. Nucleosomes and the “linker” DNA (DNA between nucleosomes) are the basic units of the chromosome fiber called chromatin. The 10-nanometer chromatin is further compacted into other higher-order structures such as the metaphase chromosomes (that is, chromosomes in the metaphase stage of the cell cycle), which are visible under a light microscope after staining.