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Stem cells & therapeutic cloning   page 3
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2. The different types of cloning Link to the Medical Research Council web site
b. Cloning to propagate (i.e. reproduce) certain plants
For example, techniques such as layering and tissue culture allow new plants to be produced that are genetically identical to existing ones. Layering has been carried out for centuries and plant tissue culture for decades. For instance, the highest yielding varieties of oil palm (Elaeis guineensis) have been cloned using tissue culture for many years to maximise the yields of oil palm oil. This oil is used in the manufacture of margarine and detergents.
Figure 3. These sheep may be clones from the same zygote.
c. Cloning to multiply up desirable embryos of farm animals
This has been carried out for a few decades and is of considerable commercial importance. For example, to clone cattle embryos, ova (eggs) are collected from a cow, semen is collected from a bull and these are allowed to mix in a petri dish in the laboratory. If zygotes are produced, in vitro fertilisation has taken place. Instead of simply placing one of the zygotes in the cow, another possibility is first of all to allow the zygote to go through a number of mitoses to produce a small embryo and then split it into two or more smaller embryos. Each of these can then be placed into a different cow. The advantage is that if you start with a top quality (e.g. high milk-yielding) cow and a top quality bull, you end up with several top quality calves rather than with just one.
Figure 4. This is Dolly, who is a clone of a single adult animal.
d. Cloning adult farm animals
Dolly the sheep was the most famous example of this. The basic procedure is to take a cell from an adult farm animal, extract the nucleus from it and then place this nucleus into an ovum of the same species that has had its own nucleus removed. This newly reconstituted cell is then placed in the uterus of a farm animal of the same species and, after a normal pregnancy, if all goes well, the animal that is born is a clone of the animal whose nucleus you started with.
e. Reproductive cloning of humans
This has not yet been carried out and is forbidden in many countries, including the UK. Were it ever to be undertaken, it would probably be done using the same approach as that to produce Dolly, described in the previous section.
f. Therapeutic cloning of humans
This is one of the ways of using stem cells and is described below. But first we need to understand what stem cells are.
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Question 2
If a human being were to be produced by the technique used to produce Dolly the sheep, would that person be identical to the individual from whom the cell was taken?