Artificial cloning in animals
In animals, only embryonic cells are naturally capable of going through the stages of development in order to generate a new individual.
We describe these cells as being totepotent sem cells, e.g. capable of differentiating into any types of adult cell found in the organism.
These cells are able to 'switch on' any of the genes present on the genome.
Splitting embroys-'artificial identical twins'
Cells from a developing embryo can be separated out, with each one then going on to produce a separate, genetically identical organism.
this methos was developed in 1979 and has been used to clone sheep, cattle, rabbits and toads.
In 2000, the first primate, a rhesus monkey called Tetra, was cloned in this way.
- they choose the desired parents e.g. high milk yield in cow and known to produce a high milk yield daughters.
- they collect the egg and the sperm and inseminate then through In vitro fertilisation (IVF)
- this grows, in vitro, into a 16-cell embryo
- they then separate this embryo into separate segments, which all produce an offspring which are all identical to each other but NOT the parents.
Nuclear transfer-using enucleated eggs
A differentiated cell from the parent can be taken, its nucleus is place in an egg cell which has had its own nucleus removed-an enucleated cell.
the egg then goes through the stages of development using genetic information from the inserted nucleus.
the first animal produced in this way was Dolly the sheep in 1996.
the cell was taken from the mammary gland of a 6-year old ewe, its nucleus transplanted into a cell from a second sheep and the inserted into the uterus of a third sheep, then a fourth to develop.
It was only successful once out of 277 attempts.
- the nucleus from a cell of the parent is removed and place into an ovum without a nucleus by Electro-fussion.
- this is then placed into a uterus to develop into an embryo
- it is then removed and placed into a surrogate embryo to develop into an offspring who is identical to the parent at the time of harvesting, so age etc. will be the same.
advantages and disadvantages
ADVANTAGE High-value animals, e.g. high milk yield, can be cloned in large numbers
Rare animals can be cloned to preserve the species. Genetically modified animals e.g. sheep that produce pharaceutical chemicals in their milk, can be quickly reproduced. DISADVANTAGES High-value animals are not necessarily produced with animal welfare in mind. Some strains of meat-producing chickend have been developed that are unable to walk.
As with plants, excessve genetic uniformity in a species makes it unlikely to be able to cope with, or adapt to changed in the environement. It is still unclear whether animals cloned using nuclear material of parent cells will remain health in the long term e.g. Dolly was put down at the age of 6 suffering from a form of lung cancer cause by a virus. Post mortem showed nothing wrong for her age, but they wrongly said that it was due to premature aging from the cloning at the time of her death.
- This is cloning cells, to generate cells tissues and organs to replace those that are damaged by disease or accident.
There are advantaged of using cloned cells;
- Being genetically identical to the individual cells mean they wont be rejected because the immune system will not recognise them.
- cloning and cell culture techniques could mean an end to currect problems of waiting for donor organs to become available for transplant.
- Cloned cells can be used to generate any cell type as they are totipotent, damage caused by some diseases and accidents cannot currently be repaired by transplantation or other treatments.
- Using cloned cells is likely to be less dangerous than a major operation such as a heart transplant.
Many possibilities include;
- regeneration of heart muscle cells following a heart attack.
- repair nervous tissue destroyed by diseases such as MS
- repairing the spinal cord of those paralysed by accident that resulted in a broken back or neck.
These are referred to as THERAPUTIC CLONING. Some object to its use in humans. lack of knowledge of how he cells will behave over time.
Turning back the clock on differentiated cells
Researchers reported they had successfully reprogrammed human skin cells to beomce pluripotents, almost identical to enbryonic stem cells, in 2008.
They identified4 essential regulator genes in this process and have called the cells INDUCED PLURIPOTENT STEM CELLS (iPS cells)
If these cells can be safelt developed from any individual's own skin cells and used to generate 200+ different cell types found in humans, the technique could replace the more controversial nuclear transfer methos used by scientists working or theraputic cloning.