Cloning, once limited to science fiction novel fantasies, became reality in 1996 with the debut of Dolly. Scottish scientist Ian Wilmut cloned Dolly, a sheep, and ethical principles behind cloning came to the forefront of scientific debates. Since Dolly’s cloning cows, goats, pigs, rats, mice, rabbits, cats, dogs, horses and mules have also been cloned. If these mammals have been successfully cloned, then why hasn’t a human?
The most commonly referenced cloning process is reproductive cloning. Reproductive cloning is defined as “the production of a genetic duplicate of an existing organism.”
Somantic cell nuclear transfer, SCNT, is the most common technique used in reproductive cloning and was used to produce Dolly. During SCNT, scientists transfer the nucleus of a body cell into an egg whose nucleus and genetic material have been removed. This is referred to as a “clonal embryo,” which is next treated with chemicals and electricity to trigger cell division.
The embryo is then placed in a female uterus where it stays until reaching full term. Part of the reason Dolly’s cloning was considered revolutionary is that prior to 1996 scientists believed embryonic stem cells were essential in cloning. Dolly was produced using an adult stem cell.
Although SCNT is the most widely used technique in cloning, successful cloning is still extremely rare. A reported 277 attempts were made before Dolly was successfully cloned. In 2004 the highest reported success rate for cloning animals was 5%, and the average was 1%. It has also been documented that as cloned animals age evident genetic problems commonly occur.