Cloning can be done by a variety of methods including natural methods such as asexual reproduction and artificial methods by cloning genes, cells or entire organisms. When a biological entity is cloned, a genetically identical copy of it is produced.
Cloning that occurs in nature can work by asexual reproduction, when single-celled organisms produce genetically identical offspring by copying a single cell from themselves. Natural cloning can also work in mammals, when a fertilized egg splits and creates identical twins that carry almost identical DNA.
Artificial cloning includes gene, reproductive and therapeutic cloning. Gene cloning is done by a different process than reproductive and therapeutic cloning and is done to produce copies of genes for researchers to study. The procedure for gene cloning involves insertion of a gene from one organism into the genetic material of a carrier where it is then multiplied in laboratory conditions.
Reproductive and therapeutic cloning share many of the same procedures, which begin by researchers removing a mature somatic cell from the organism that they wish to copy. The DNA from the somatic cell is then transferred into an egg cell that has its own DNA removed. The egg is then allowed to develop into an embryo in a test tube and is either implanted into the womb of an animal or is used for therapeutic research. When the animal gives birth, the offspring has the same genetic composition as the animal the somatic cell was taken from.