Free Natural and Artificial Cloning in Animals OCR A Level Biology revision notes – covering specification points 6.2.1(c), 6.2.1(di) and 6.2.1(dii).
Natural Cloning in Animals
Natural cloning in animals can occur through modifications to embryo formation or development (e.g. identical twins), budding (e.g. hydra), or fragmentation (e.g. planarians).
Artificial Cloning in Animals
Artificial cloning is used to produce genetically identical cells, tissues, organs or whole organisms.
Artificial cloning in animals may be reproductive or non-reproductive:
- Reproductive cloning produces whole, genetically identical animals.
- Non-reproductive cloning* produces genetically identical cells and tissues for medical uses.
*Also known as therapeutic cloning.
Reproductive Cloning
Reproductive cloning can be carried out by artificial embryo twinning and somatic cell nuclear transfer:
- Artificial embryo twinning involves splitting an early embryo to produce two or more genetically identical embryos.
- Somatic cell nuclear transfer (SCNT) involves transferring the nucleus of a somatic cell into an egg cell whose own nucleus has been removed.
Artificial Embryo Twinning
Artificial embryo twinning involves manually splitting an embryo into two (or more) clusters of cells to create two (or more) genetically identical embryos.
A simplified method for artificial embryo twinning is outlined below:
- Produce a zygote by in vitro fertilisation (IVF).
- Allow the zygote to divide by mitosis into a small ball of cells, forming an early embryo whose cells are still totipotent.
- Split the embryo into two or more smaller embryos.
- Implant each embryo** into a surrogate mother, where it develops into an individual. The resulting offspring are genetically identical to one another.
**One embryo can be saved to be further divided into more embryos while its cells remain totipotent, allowing additional genetically identical embryos to be produced.
Somatic Cell Nuclear Transfer (SCNT)
Somatic cell nuclear transfer (SCNT) produces a clone from a single somatic cell of the animal to be copied.
The somatic cell contains the genome of the organism to be cloned within its nucleus, which is removed and fused with an egg cell that has been enucleated (had its nucleus removed).
A simplified method for somatic cell nuclear transfer is outlined below:
- Remove the nucleus from an egg cell.
- Remove a nucleus from a somatic cell of the animal being cloned.
- Fuse the somatic cell nucleus with the enucleated egg cell using an electric shock*.
- The electric shock stimulates the egg cell to begin dividing.
- Allow the cell to divide and develop into an embryo.
- Implant the embryo into a surrogate mother and allow it to develop.
*The electric shock also stimulates the egg cell to begin dividing.
Arguments For and Against Artificial Cloning in Animals
The table below outlines some of the advantages of artificial cloning in animals:
| Advantage | Explanation |
|---|---|
| Medical treatment | Genetically identical tissues or organs could be grown to treat injuries or diseases in patients, eliminating the risk of rejection. |
| Reproduction of high-value animals | Large numbers of identical, high-value animals can be produced by selective breeding (e.g. a cow with a high milk yield), or genetic modification, and then cloned. |
The table below outlines some of the disadvantages of artificial cloning in animals:
| Disadvantage | Explanation |
|---|---|
| Expensive | High costs due to the need for trained personnel and the low success rate. |
| Poor health | Cloned animals have a much higher risk of health issues and a shorter lifespan. |