A cell, group of cells, or organism that is produced asexually from and is genetically identical to a single ancestor. The cells of an individual plant or animal, except for gametes and some cells of the immune system, are clones because they all descend from a single fertilized cell and are genetically identical. A clone may be produced by fission, in the case of single-celled organisms, by budding, as in the hydra, or in the laboratory by putting the nucleus of a diploid cell into an egg that has had its nucleus removed. Some plants can produce clones from horizontal stems, such as runners. Clones of other cells and some plants and animals can also be produced in a laboratory. See also therapeutic cloning .