1. A group of cells, an organism, or a population of organisms arising from a single ancestral cell. All members of a particular clone are genetically identical. In nature clones are produced by asexual reproduction, for example by the formation of bulbs and tubers in plants or by parthenogenesis in certain animals. New techniques of cell manipulation and tissue culture have enabled the cloning of many plants and some animals. A wide range of commercially important plant species, including potatoes, tulips, and certain forest trees, are now cloned by micropropagation, resulting in more uniform crops. Cloning in animals is more complex, but has been accomplished successfully in sheep, cattle, and various other species. The first mammal to be cloned experimentally from the body cell of an adult was a sheep (‘Dolly’) born in 1997 after over 200 previous failed attempts. The nucleus containing DNA was extracted from an udder cell (which had been deprived of nutrients) and inserted into an ‘empty’ egg cell (from which the nucleus had been removed) using the technique of nuclear transfer. This reconstituted egg cell was then stimulated to divide by an electric shock and implanted into the uterus of a surrogate mother ewe, who subsequently gave birth to a clone of the original sheep. This breakthrough has led to the production of exact replicas of animals with certain genetically engineered traits, for example to manufacture drugs in their milk or provide organs for human transplantation. Cloning may also be used to perpetuate endangered species, where rates of natural reproduction are dangerously low, or even to replicate pet animals for doting owners.

2. (gene clone) An exact replica of a gene. See gene cloning.