Cloning.

In 1997 Ian Wilmut at the Roslin Institute in Scotland successfully cloned a sheep named Dolly from the cell of an adult ewe. Wilmut replaced the DNA in a normal sheep egg with the DNA from the ewe's mammary gland, and then inserted the egg into the womb of another sheep, where it grew into an exact replica of the donor. This achievement was the first time that an animal had been cloned from an adult cell, not an embryo. It was a milestone in genetic engineering, indicating that it was possible to mass produce identical copies of a mammal. Many people worried about the ethical implications of this new technology, since the same techniques used to make Dolly might one day be used to clone humans. In 1993 researchers at George Washington University had cloned human embryos and nurtured them in a petri dish...