Group Creates Engineered 'Marathon Mice' SAN FRANCISCO - Researchers on Monday unveiled genetically engineered mice that can run farther and longer than their naturally bred brethren, bringing the "genetic doping" of elite athletes a small step closer to reality.    The creation of the so-called marathon mice, announced Monday, follows earlier genetic engineering work that created "Schwarzenegger mice," rodents that bulked up after getting injected with muscle-building genes...