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chromosome chro·mo·some (krō'mə-sōm')
A threadlike linear strand of DNA and associated proteins in the nucleus of animal and plant cells that carries the genes and functions in the transmission of hereditary information.
A circular strand of DNA in bacteria and cyanobacteria that contains the hereditary information necessary for cell life.
A structure in all living cells that consists of a single molecule of DNA bonded to various proteins and that carries the genes determining heredity. In all eukaryotic cells, the chromosomes occur as threadlike strands in the nucleus. During cell reproduction, these strands coil up and condense into much thicker structures that are easily viewed under a microscope. Chromosomes occur in pairs in all of the cells of eukaryotes except the reproductive cells, which have one of each chromosome, and some red blood cells (such as those of mammals) that expel their nuclei. In bacterial cells and other prokaryotes, which have no nucleus, the chromosome is a circular strand of DNA located in the cytoplasm.
The small bodies in the nucleus of a cell that carry the chemical “instructions” for reproduction of the cell. They consist of strands of DNA wrapped in a double helix around a core of proteins. Each species of plant or animal has a characteristic number of chromosomes. For human beings, for example, it is forty-six.
Note: In humans, sex is determined by two chromosomes: an X-chromosome, which is female, and a Y-chromosome, which is male. (See sex chromosomes.)