1. Ewe were always on my mind….
Title: Clones in animals
Homework: learning package 11 due in today
Ewe were always on my mind….

2. Learning Outcomes
(e) describe how artificial clones of animals can be produced; (f) discuss the advantages and disadvantages of cloning animals (HSW4, 6a, 6b, 7c).

3. Stem Cells
All cells start of with the same DNA, so why do they end up looking so different?
Some genes “switch on” while others “switch off”, leading to a process called differentiation.
Cells that have differentiated cells lose their ability to divide and produce more cells of different kinds.

4. Stem Cells What happens to cells that remain undifferentiated?
These undifferentiated cells are called stem cells – they have the ability to become any other cell in the body (or more stem cells).
Why is this useful?

5. Obtaining stem cells - embryos
Most useful at a few days old – ball of undifferentiated cells.
Cells at this stage are totipotent – divide to form a whole new organism!
cell stage is described as pluripotent – ability to become any cell type, but not a new organism because some cell differentiation has already started.

6. Totipotent cells can divide to form a new organism
Stem cells
Embryonic stem cells
Totipotent cells can divide to form a new organism
Pluripotent cells can divide to form any other specialised cells of any type

8. Embryo formation
Embryo is formed by transferring DNA from embryonic stem cells to an egg whose nucleus has been removed (enucleated).
Reconstructed egg containing DNA from a donor cell is treated with an electric current to stimulate cell division and blastocyst formation.

9. Cloning by nuclear transfer

10. Cloning by splitting embryos

11. What are the differences between cloning by splitting of embryos and cloning by nuclear transfer?
The nucleus comes from an egg fertilised in vitro and allowed to divide to form an embryo
The embryos produced are clones of the original zygote
The zygote is a product of a fertilised egg. Since this is formed from fusion of sperm and egg cells which are themselves a product of meiosis, it is impossible to know exactly what characteristics the cloned organism will possess
All cellular components are derived from the original zygote. The mitochondrial DNA component will be identical in each clone
Nuclear transfer
The nucleus comes from an adult, differentiated cell taken from the animal to be cloned
The embryos produced are clones of the donor adult organism
The adult cell is a product of an adult with known characteristics. It is therefore known what characteristics the clones will possess
The cellular components are derived from the egg cell used therefore the mitochondrial DNA component will be different from that of the original adult cell

12. Reproductive vs non-reproductive
Reproductive cloning
Cloning to produce a whole organism
Examples
Embryo transplantation
Dolly the sheep
Non-reproductive cloning
Using cloning to produce cells
Examples
Stem cell research
Production of cells, tissues or organs

13. Dolly the Sheep
Dolly the sheep is believed to have suffered from a serious health problem which developed at a relatively early age

14. Non-reproductive cloning in animals
Non-reproductive cloning involves the production of genetically identical cells
1951 – HeLa cells
Cancerous cells which divide repeatedly in culture solution
Used in medical research
Stem cells
Totipotent or pluripotent
Undifferentiated cells that are able to differentiate into specialised cells
Embryonic stem cells – ethical arguments

15. Possibilities of non-reproductive cloning
Potential future uses include
Regeneration of heart tissue following a heart attack
Repair of nervous tissue
Repairing the spinal cord
Stem cells taken from the patient to produce the tissues mean that tissue rejection by the immune system is less likely

16. Advantages and disadvantages of cloning animals
High-value animals, for example cows giving high milk yield, can be cloned in large numbers
High-value animals are not necessarily produced with animal welfare in mind. Some strains of meat-producing chickens have been developed that are unable to walk
Rare animals can be cloned to preserve the species
As with plants – excessive genetic uniformity in a species makes in unlikely to be able to cope with, or adapt to, changes in the environment
Genetically modified animals – for example sheep that produce pharmaceutical chemicals in their milk – can be quickly reproduced
It is still unclear whether animals cloned using the nuclear material of adult cells will remain healthy in the long term. Dolly was put down at 6 years old due to lung cancer caused by a virus, although post-mortem showed nothing unusual

17. Artificial Cloning in animals
Advantages
High value animals
Rare animals can be cloned
Quickly reproduced
Disadvantages
Animal welfare
Genetic uniformity, loss of genetic variation
Uncertainties of health of cloned animals
Moral and ethical Arguments
Is it right to clone an aging pet?
Is it right to clone an animal which leads to a
cure for human diseases?

18. Give reasons why repairing a damaged heart using cloned cells could potentially be less dangerous than receiving a heart transplant
Heart transplant surgery carries with it risk of infection associated with any major surgery.
There are also risks associated with use of general anaesthetic.
The transplanted heart is foreign tissue – as such it may be rejected by the host’s immune system.
Cloned cells are derived from the host and it may be possible to get them to the right location using relatively minor surgical methods