Different Cloning Techniques
Since the successful and very public birth of Dolly the sheep in 1996, cloning has received significant attention and is considered a controversial topic by some. The controversies that surround cloning however, are generally related to reproductive cloning. Several other cloning techniques exist, each with a vastly different process and result. Regardless of the type of cloning used, cloning requires a cell with intact DNA. Despite controversy, cloning remains a pivotal area of research in the 21st century.
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DNA Cloning
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The process of DNA cloning is the most common type of cloning and is relied upon in many research and laboratory settings. DNA cloning involves extracting a wanted DNA fragment and transferring the fragment to a self-replicating cell. Often, bacterial plasmids are used as the DNA host, copying the DNA into several identical fragments. This allows scientists to study a certain gene with greater speed and accuracy, as many genes are rare and hard to extract from a DNA sequence. The technology behind DNA cloning was developed in the 1970s. DNA cloning is also known as recombinant DNA technology and molecular cloning.
Embryo Splitting
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Embryo splitting refers to the process of splitting an eight-cell embryo into singular cells. Two of these cells, or blastomeres, are then transferred into a zona pellucida (a membrane surrounding an immature ovum) to create a new embryo. Once the cell reaches the blastocyst stage, stem cells can be obtained from the inner cell mass for use in additional research. Embryo splitting has been used to successfully clone primate cells, but is somewhat less common as a cloning method than Somatic Cell Nuclear Transfer.
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Somatic Cell Nuclear Transfer
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Somatic Cell Nuclear Transfer (SCNT) is a cloning process usually used to produce a genetic duplicate of an existing organism. In SCNT, a nucleus from any adult cell in an organism's body is extracted, then inserted into an egg cell that has had its nucleus removed. The cell is then cultured until it reaches the blastocyst stage, and implanted into a surrogate mother to develop normally. The chromosomes within this new organism will be identical to that of the organism from which the nucleus was taken. Alternatively, embryonic stem cells can be harvested at the blastocyst stage for further research.
Reproductive vs. Therapeutic Cloning
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Depending on the process, the use of Somatic Cell Nuclear Transfer is often referred to as reproductive or therapeutic cloning. When SCNT is used to produce an embryo not intended for implantation in a surrogate, this is known as therapeutic cloning. Therapeutic cloning is used solely to produce embryonic stem cells for scientific research. On the other hand, reproductive cloning refers to the process of using SCNT to create a living genetic duplicate of an organism.
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