Yang worked tirelessly to promote cooperation between U.S. and Chinese researchers, particularly in cloning and other areas of biotechnology, and established a nonprofit company to export cloned embryos from prize dairy cattle to China to increase the supply of milk.

He was also a committed advocate for human cloning as a technique to produce stem cells for medical use.

As a young faculty member at Cornell University in the early 1990s, Yang had tried unsuccessfully to clone rabbits, and he, like many others at the time, had begun to doubt the possibility of cloning using cells from adults.

But the announcement in Scotland on July 5, 1996, that Dolly the sheep had been cloned renewed his vigor, and in 1998, by then working at the University of Connecticut, he collaborated with Japanese researchers to clone six calves from a prized bull.

The next year, he announced the birth of Amy, the first farm animal cloned in the United States.