Cloning: Background A clone is a group of genetically identical cells. For example, tumors are clones of cells inside an organism because they consist of many replicas of one mutated cell. Another type of clone occurs inside a cell. Such a clone is made up of groups of identical structures that contain genetic material, such as mitochondria and chloroplasts. Some of these structures, called plasmids, are found in some bacteria and yeasts. Techniques of genetic engineering enable scientists to combine an animal or plant gene with a bacterial or yeast plasmid. By cloning such a plasmid, geneticists can produce many identical copies of the gene