ABSTRACT
Genetic manipulation is now a standard tool for biologists interested in understanding gene function in health and disease. This can take the form of adding genetic material to an organism (a transgene) or modifying the expression of endogenous genes (knockout or knock-in experiments). The majority of such studies involves the modi¿ cation of cells in culture or the modi¿ cation of the reproductive cells of animals, mostly mice, so that the modi¿ cation is expressed in all of the cells of a tissue (e.g. muscle) and the modi¿ cation is heritable. However, it is also possible to modify nonreproductive (somatic) tissues in the mature animal. The latter technology, which is mostly intended for genetic therapies of inherited or acquired disease, raises the possibility of genetic manipulation for increased sporting performance (gene doping).
