Cloning is a form of asexual reproduction, the creation of genetically identical genes, cells, plants, or animals. Cloning can take many forms, including taking the DNA of a mature organism and introducing it into an egg cell, which then grows up genetically identical to its donor. Cloning also takes place naturally in bacteria and yeast, and when twins occur. In this case, a fertilized egg cell in the course of its many divisions creates two organisms rather than one.