- Cloning envisioned. Dr. Hans Spemann (Germany) proposed an experiment to remove the nucleus from an unfertilized egg and replace it with the nucleus from a differentiated cell.
- Structure of DNA (deoxyribonucleic acid) discovered by Francis C. Crick (U.K.) and James D. Watson (U.S.).
- Dr. John B. Gurdon (U.K.) clones a frog by transplanting the intestinal cell of a tadpole into an enucleated frog egg, which develops into an adult frog.
- First successful gene splicing (recombinant DNA) by Paul Berg and Stanley N. Cohen (U.S.). A major breakthrough in genetic engineering.
- Birth of first child, conceived by in vitro (literally “in glass”) fertilization to Leslie Brown (U.K.).
- U.S. Supreme Court rules that a genetically created new bacterium (a non-natural manmade microorganism) may be patented.
- Dr. Steen M. Willadsen (Denmark) clones a lamb from a developing sheep embryo cell. His experiment is repeated by other scientists who clone a variety of animals.
- Dr. Ned First (U.S.) clones calves from cells of early embryos.
- Drs. Ian Wilmut and Keith Campbell (U.K.) create the world's first cloned sheep, Megan and Morag, from embryo cells.
- Dr. Ian Wilmut and his team clone the world's the first sheep from adult cells. The lamb born in July 1996 is named Dolly.
- Scientists at Oregon Regional Primate Research Center (U.S.) create first primates—two rhesus monkeys named Neti and Ditto—from DNA taken from cells of developing monkey embryos. They are not genetically identical because two different embryos were used.
- A team led by Drs. Ian Wilmut and Keith Campbell (U.K.) create the first sheep with a human gene in every cell of its body. The genetically engineered lamb is named Polly.
- Dr. Gerald Schatten (U.S.) leads a team of researchers who become the first to create a clone (Tetra, a rhesus monkey) by embryo splitting.
- Dr. Xiangzhong Yang leads a U.S. experiment to clone calves from frozen cells taken from a Japanese bull. The experiment is successful and proves that cells can be stored for later cloning.
- The first patents for cloning are given to the scientists who cloned Dolly, giving their company, Geron Bio-med, exclusive right to the technologies they used.
- Japanese scientists clone a baby bull from a bull that was a clone itself, the first re-cloning case involving a large mammal.
- Five piglets are cloned by a company the eventually wants to reproduce organs for humans.
- Scientists at Advanced Cell Technology in Massachusetts clone human embryos for the first time.
- President Bush limits federally funded human embryonic stem cell research to stem cell lines that have already been created.
- A cat, called C.C. for “carbon copy” is cloned by a company that wants to go into business reproducing pets.
- California becomes the first U.S. state to approve a law legalizing the therapeutic cloning of embryos.
- Britain becomes the first country to issue research licences for human embryonic cloning to create stem cells. It specifies therapeutic, not reproductive, cloning.
- Britain announces the first embryonic stem cell bank.
- South Korea clones a dog named Snuppy. Dogs are considered particularly difficult to clone because of the complex reproductive biology.
- South Korea announces that in 2005, cloned wolves were born. In Japan, a fourth-generation pig was cloned, proving that a mammal can be cloned for multiple generations.
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