There are various ways to "Clone" living organisms. The following text explains the main genetic techniques used in cloning today. The research carried out at the Roslin Institute is the first in which the complete genetic material from an adult mammalian cell has been used in the development of an identical new individual. The technique involves several steps.

First, the donor cells are grown under special conditions in culture. In this way the number of cells can be increased by several orders of magnitude. It is also possible to make genetic modifications and to select just those cells in which the desired modification has occurred. The selected cells are then fused with an unfertilised egg from which the introduced nucleus can lead to the formation of an embryo. The embryos are then transplanted into female sheep and the lambs are born naturally.

The simplest way to make clones is making twins, which have the exact same DNA. This can be achieved by separating the embryo and duplicating one into two. Using this technique one can make perfectly identical twins. Embryo splitting or blastomere separation is what is most commonly referred to as human cloning. Embryos in the early stages of development start to divide into cells called blastomeres. The zona pellucida (a protective covering for the egg) is punctured or removed and the blastomeres are separated from each other. Each blastomere is then covered with an artificial zona pellucida. Then each of the blastomeres starts dividing and becomes an embryo. This was attempted by Hall and Stillman in 1993. They used embryos that contained too much genetic information and got as far as 32-cell divisions in some the embryos. At this stage the embryo can be implanted in the womb. In theory it is possible to make triplets, quadruplets and even more using the same method. But in reality it is impossible to make more than four duplicates from one embryo. Trying to make more than four clones at the same time results in the death of the embryos. This technology has been used for stockbreeding for many years.
 

By using this technology, unlike the way to make clones from separating the embryo it is possible to make many life forms that have the exact same DNA. In this process unspecialized embryonic cells are used and their nuclei are removed. An embryo in the 32-cell division stage has its blastomeres separated and then the blastomere is fused with an egg cell by using an electric current or another method. First, a healthy cell or a fertilized egg is taken from the body of the original. The cell is then transferred into an unfertilized ovum where it is allowed to grow. There are 2 basic ways for cloning by nuclear transplantation depending on where the original cell is taken from. These are:

The other way to obtain DNA is by taking a sample cell from part of the body that is of interest for cloning. This can be a cell or a tissue taken from the liver of a mammal. However, cells are usually taken from the ear or the skin. The same procedure as using the cell from a fertilized ovum is followed as above to produce a clone. Dolly can be used as an example to this technique of taking a cell from parts of the body.
 

First, the cell is taken from a fertilized ovum. When the cell starts to split up it is taken out of the cell and replaced into another unfertilized ovum. Then the ovum is placed into a different mammal. All the clones will possess the same DNA as their original donor.

Links to Other Techniques of Cloning are:

Nuclear Transfer -- no link available

The Roslin Technique -- as briefly descibed above

The Honolulu Technique

Learning the Genetic Code

Recombinant DNA

Polymerase Chain Reaction

X-ray Crystallography