The biology of cloning.

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AS level Biology Coursework

Cloning

Cloning has received a lot of interest recently, with the death of Dolly the sheep, ‘the first mammal ever created from the non-reproductive tissue of an adult animal’, and whether her death had anything to do with the fact that she was a clone, as well as the current rumours over human clones and the moral issues involved with it.  

Cloning involves a process called nuclear transfer, which was first explored by Spemann in the 1920's to conduct genetics research. All cloning experiments of adult mammals have used a variation of nuclear transfer. Nuclear transfer requires two cells, a donor cell and an oocyte, or egg cell. Research has proven that the egg cell works best if it is unfertilized, because it is more likely to accept the donor nucleus as its own. The egg cell must be enucleated.

The nucleus is removed from the egg cell. This removes the majority of its genetic information. The donor cell is then forced into the Gap Zero, or G0 cell stage, a dormant phase, in different ways depending on the technique. This dormant phase causes the cell to shut down but not die. In this state, the nucleus is ready to be accepted by the egg cell. The donor cell’s nucleus is then placed inside the egg cell, either through cell fusion or transplantation. The egg cell is then prompted to begin forming an embryo. Then, the embryo is transplanted into a surrogate mother. If all is done correctly, there is a small chance a perfect replica of the donor animal will be born, ‘…it later emerged that Dolly was the sole success from almost 300 attempts at the Roslin Institute to clone embryos.’ – Focus Magazine December 2002 

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The cloning of Dolly has been the most important event in cloning history. Not only did it spark public interest in the subject, but it also proved that the cloning of adult animals could be accomplished. Previously, it was not known if an adult nucleus was still able to produce a completely new animal. Genetic damage and the simple deactivation of genes in cells were both considered possibly irreversible. "Three years ago we didn't think it could be done," said Ian Wilmut, one of the team from the Roslin Institute

The realization that this was not the case came after ...

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