July 1997, Ian Wilmut and colleagues announced the production of lambs containing a human protein that produces a particular blood protein by first inserting the human gene into a sheep fetus cell. After cell division had occurred, nuclear transfer was carried out. Two identical lambs with the human gene survived the process. These transgenic animals can potentially be used to treat several diseases, including in this case, hemophilia.
 

August 1997, scientists in Wisconsin report a more efficient cloning procedure than that used to produce Dolly. After the first nuclear transfer of calf cells, the scientists performed a second nuclear transfer before placing the resultant embryo in the surrogate mother, so as to make the nucleus in the embryo more susceptible to reprogramming, increasing the success rate of the procedure. Compared to Dolly, only 15 attempts were required to produce a healthy calf. However, in this experiment, the nucleus was obtained from a fetus.
 

July 1998, biologists at the University of Hawaii announce that by varying the cloning procedure used to produce Dolly, they were able to create more than 50 mice using adult cells. Instead of starving the somatic cells in culture, the scientists used naturally dormant cells surrounding eggs in ovaries, so that they were easily reprogrammed. Also, instead of applying an electri shock to the cells to fuse them together, the scientist used an extra-fine needle to inject the nucleus of the dormant cell into the enucleated cell, causing less damage to the egg and increasing the likelihood of developing a healthy embryo. Because mouse and human development are very similar, this experiment suggested that humans could all the more be successfully cloned.
 

June 1999, scientists at Advanced Cell Technology announce the first successful cloning of a human embryo. The scientists injected DNA from a human leg cell into a cow egg. The embryo developed successfully for 12 days before it was destroyed, as embryos are seen as being human only after 14 days. The results are promising for researchers who are trying to find a way to cultivate stem cells, which can be used to treat many diseases.
 

August 1999, study on Dolly's cells show that her telomeres, the tips that protect chromosomes, were showing premature signs of wear and tear, mostly likey because her genetic material originally came from an ewe that was 6 years old. Cell division places much stress on telomeres, so that during aging the telomeres become too frayed to protect the chromosomes, and the cell dies. This raised questions about whether cloned animals might die prematurely, and the effectiveness of using cloned cells for medical treatment.
 

August 2000, researchers from the University of Tennessee clone cows using routine laboratory cell-culture methods so that it was not necessary to slow the development of the egg cells required in cloning. This technique, compared to that used to produce Dolly, is much faster and less complicated, which would make cloning a much cheaper process.
 

September 2000, researchers at the University of Hawaii and the Rockefeller University of New York show that cloning does not necessarily produce clones with shorter telomeres. The researchers cloned mice through 6 generations, but not only did the cloned mice show no signs of premature aging, but some of the cloned cells showed signs of getting younger.