Many somatic plant cells, including some fully differentiated types (e.g. leaf mesophyll),provided they contain intact nuclear, plastid and mitochondrial genomes, have the capacity to regenerate into whole plants. This phenomenon is totipotency.Totipotent cells from plants have been used in tissue-culture techniques to produce improved plant materials that are pathogen-free and disease-resistant. Totipotent cells fromanimals are now being used to clone mammals, although ethical questions remain overwhether cloning a human should be done. Cell potency is a cell’s ability to differentiate into other cell types. The more cell types a cell can differentiate into, the greater its potency. Potency is also described as the gene activation potential within a cell which like acontinuum begins with totipotency to designate a cell with the most differentiationpotential, pluripotency, multipotency, oligopotency and finally unipotency.