Clones are organisms that are exact genetic copies. Every single bit of their DNA is identical. Clones can happen naturallyidentical twins are just one of many examples. Or they can be made in the lab. Below, find out how natural identical twins are similar to and different from clones made through modern cloning technologies. Many people first heard of cloning when Dolly the Sheep showed up on the scene in 1997. Artificial cloning technologies have been around for much longer than Dolly, though. The term cloning is used by scientists to describe many different processes that involve making duplicates of biological material. In most cases, isolated genes or cells are duplicated for scientific study, and no new animal results. The experiment that led to the cloning of Dolly the sheep in 1997 was different: It used a cloning technique called somatic cell nuclear transfer and resulted in an animal that was a genetic twin although delayed in time of an adult sheep. This technique can also be used to produce an embryo from which cells called embryonic stem (ES) cells could be extracted to use in research into potential therapies for a wide variety of diseases. There are two ways to make an exact genetic copy of an organism in a lab: artificial embryo twinning and somatic cell nuclear transfer. This encyclopaedia will be an essential reading for anyone interested in cell biology or introductory biology.