Mice may have been the first animals to reap the effects of gene doping, growing larger and stronger than mice not injected with genes in lab experiments. 

GK Hart/Vikki Hart/­Getty Images

­Maybe you saw the "mighty" mice. After being injected with a muscle-preserving gene, some of these mighty rodents maintained the muscles of youthful mice, at the human equivalent of age 80, without exercise [source: Cromie]. Did that news story escape your notice? Well, maybe you heard about the healthy monkeys who, when injected with a blood-making gene, dramatically increased their red blood ­cells and, consequently, could carry more oxygen in their bodies [source: Svensson].

One day, it's mice and monkeys; the next, professional athletes. After hearing of these gene injection experiments, coaches and athletes have called the scientists, asking to volunteer as subjects [source: Reynolds]. So is it possible to "dope" with genes? Will athletes try it by the 2012 Olympics, or have they already begun doctoring their DNA?

First, let's be clear about gene doping. The World Anti-Doping Agency (WADA), whose drug code governs the Olympics and other events, defines gene doping as "the non-therapeutic use of cells, genes, genetic elements, or the modulation of gene expression, having the capacity to enhance athletic performance" [source: WADA]. That's a mouthful. A simpler definition might read adding or altering genes in otherwise healthy people to adapt the body for sports.

­Gene doping, as its name suggests, differs slightly from gene therapy. Gene therapy is used for illnesses, in which the injected gene compensates for one that's absent or not working. It's a matter of usage; the techniques for gene doping and gene therapy are more or less the same.

As far as we know, no athlete has tried gene doping, says Dr. Theodore Friedmann, a University of California San Diego professor who also heads WADA's panel on gene doping. But he says it's inevitable. And against sporting rules, too. WADA and the International Olympic Committee banned gene doping in 2003 [source: WADA].

Read on to find out how athletes might tamper with their genes and to what end.