Cloning, in broad terms is the process of making an exact copy of something. In terms of biology it refers specifically to making an exact copy of DNA, Cells or whole Organisms. Cloning has many uses but since all of the other articles focus on reproductive cloning and in particular mammalian cloning, so will I. I write this article not to give my opinion but to present the facts about cloning.
Cloning is a time consuming and rather expensive process in which Donor DNA is taken from a somatic cell (any body cell that is not a reproductive cell like sperm or egg) and implanted into a donor egg that has had its own DNA removed. Somatic cells contain a complete set of DNA, which has two copies of each chromosome as opposed to a germcell which only has one. The donor egg is then implanted in an unrelated surrogate mother to complete development inside the womb. The resulting individual is then an exact copy of their mother or father.
Naturally any article about cloning will have some reference to Dolly the Sheep. While cloning has therapeutic uses in the control of disease and possibilities in deriving organs from stem cells the drawbacks appear to outweigh them. Premature aging of clones is a significant problem that all research has encountered. Dolly lived just six years, but what people forget is Dolly's mother was 6 when the DNA used to create Dolly was obtained. This means that Dolly was actually 12 when she died, the average age of a sheep. Our cells can only undergo a certain amount of replications and this is what causes us to age. Each time DNA is replicated a little bit is cleaved and when DNA can no longer be replicated death is imminent. So at birth Dolly was genetically 6 and she aged naturally. Another article suggests that "X Chromosome Dominance" and the lack of mosaics caused the premature death of Dolly. I can't find anything in the literature on this either because it is not technically correct. To my knowledge there is no such thing as X Chromosome Dominance, there is however Gene Dominance which can occur on either Somatic cells or Germcells but has no bearing on cloning. I don't want to go into this because it is quite complicated and not necessary.
The recent cloning of "Snuppy the Puppy" in South Korea highlights just how ineffective cloning is. Researchers used 1,095 embryos with Donor DNA and implanted them into 123 surrogate mothers. However out of these only 3 resulted in pregnancy, one of which miscarried, another died of pneumonia and the third had a successful birth. This means that there is a 0.09% chance that the cloning will be successful and that 99.91% of the time it fails.
Another point that has failed to be mentioned is the emotional side to cloning. Everyone always thinks about the physical things that can go wrong with cloning. When talking about human cloning you have to ask yourself why people want to clone. Are they seeking comfort in death knowing that they can recreate a loved one? If so, a clone could never be the same as the original. How do you ensure they have all of the same experiences that shaped their Donor's life? How do we know that trivial things like the colour of your family couch or the placement of photos don't affect the way people develop? While you can clone the body, you can never clone the mind.