Meanwhile, researchers are hoping to develop transgenic pigs whose hearts and kidneys could be transplanted to needy humans. Transgenic technology could also help in treatments for emphysema and burn victims. Because creating transgenic animals is extremely difficult and costly, even more difficult and costly than cloning, researchers are hoping to use cloning techniques to make multiple copies of the transgenic animals they make.

Cloning could also revolutionize animal testing by reducing the number of animals required to test an effect. Cloned test animals could eliminate the variability cause by genetic differences and provide clearer results, even with many fewer animals.

Another potential benefit--in fact, the original aim of the Dolly experiment--would be to increase food yields from livestock and crops. Selective breeding has long been used to increase food yields, but cloning could speed the process by making it possible to make multiple copies of, for example, the perfect tomato plant. On the down side, cloning of livestock or crop plants would weaken the genetic diversity that keeps animal populations safe from catastrophic epidemics.