Cloning involves making one or more genetic replicas of a cell or organism.

Identical Twins: Fertilized eggs may be induced to split very early in development to create identical twins, which are clones.

Creating Clones from Differentiated Cells: Early during embryo development, cells differentiate into the cell lineages they are to become. Thus cells become nerve cells, stomach cells, skin cells, etc. Such differentiated cells may not easily be changed to other cell types. However, a technology using differentiated cells to clone individuals is currently being experimented with. This process is known as Nuclear Transfer Technique.

1. Udder cells are taken from the udder of a donor sheep and cultured in a low nutrient culture to stop the cells from dividing. Dormant udder cells are needed for step 3.

2. An unfertilised egg is removed from the ovary of another sheep. The nucleus of this egg is removed using a micropipette.

3. The remaining portion of the egg lacks a nucleus but contains cytoplasm and the cellular machinery for producing an embryo.

4. The dormant udder cell and egg cell lacking the nucleus are placed together in a culture dish. A gentle electric pulse causes the 2 cells to fuse.

5. A time delay then allows the chromatin to become activated.

6. A second electric pulse stimulates cell division and cell activity.

7. Mitosis forms a small ball of embryonic cells.

8. After about 6 days,the embryo is surgically implanted into the uterus of the surrogate mother, another sheep.

9. If the implanted embryo takes, the pregnant ewe will give birth after about 150 days to a lamb (Dolly) that is genetically identical to the original donor.

[Diagram illustrating the cloning of a sheep]

The Cloning of Dolly

Dolly was world's hello to cloning's possibilities (USA Today)

[Gene Cloning]