cloning (general): replicating and propagating the genetic makeup of an organism, either partially or completely. There are several different types of cloning (see below)
clone (cell culture): a population of cells derived from a single cell by cell division (mitosis). The clone is seen as a clump of cells in the cell culture dish. The cells in a cell culture clone are not necessarily identical
clone (plants): may refer to a cultured clone (as above), or to a group of plants derived by propagation from a single individual through cuttings or other asexual means
clone (bacterial): the unicellular progeny of a single bacterial cell. When grown on agar in petri dishes, bacterial clones form clusters (colonies)
molecular or DNA cloning: copying a particular sequence of DNA, and transferring it to a different cell (usually bacterial or yeast) using a DNA vector (usually a plasmid, phage or similar), where it is copied along with the rest of the cell’s DNA when the cells divide. This method can be used to produce large quantities of the product of the DNA sequence (e.g. to produce insulin). See also Recombinant DNA technology
cloning (animals): a type of reproduction in which the complete genotype of an animal is copied, generally by replacing the nuclear DNA of an egg cell from a host with the nuclear DNA of a body (somatic) cell from the donor organism (a process called somatic cell nuclear transfer). ‘Dolly’ the sheep was created in this way
therapeutic cloning: a method to obtain perfectly matched human embryonic stem cells from an individual. These cells have the potential to become tissue-specific cells that can be transplanted back into the individual to repair damaged cells or tissues without risk of rejection. The technique involves somatic cell nuclear transfer – the same technique that created Dolly the sheep – but the cloned egg cell containing the individual’s DNA is only allowed to form a small cell cluster (blastocyst), the inner layer of which is rich in stem cells. These stem cells are removed and used to create the specific cell type(s) required