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| Vectorless Gene Transfer |
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| Gene transfer can be effected by certain means that do not use vectors. These include |
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| a. Electroporation: Temporary holes are formed in the plasma membrane of the host cell by applying a high voltage. These pores permit entry of foreign DNA. |
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| b. Chemical mediated genetic transformation some chemicals, such as polyethylene glycol, help foreign DNA to enter the host cell. |
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| c. Micro-injection: The host cell is immobilized by applying a mild suction with a blunt pipette. The foreign gene is then injected with a micro-injection needle. |
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| fig. 25.3 Introduction of Foreign DNA in a Host Cell with a Microinjection Needle |
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| d. Particle gun: Tungsten particles coated with foreign DNA are bombarded into the host cell. |
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| 1. To understand molecular events in biological processes such as cell differentiation and aging. |
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| 2. It can be used to make precise gene maps. |
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| 3. Useful chemical compounds can be produced example: injectable hepatitis B vaccine. |
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| 4. It has provided a broad range of tools to aid physicians in the diagnosis of diseases. |
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| Example: |
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| a. Identification of food poisoning by Salmonella, |
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| b. Hepatitis virus |
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| c. HIV |
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| 5. Testing the DNA of parents who are carriers for genetic disorders can be done and other chances of producing an afflicted child can be predicted. |
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| It means to replace a faulty gene by a normal healthy functional gene. |
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| Example: |
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| Severe Combined Immuno Deficiency (SCID). This disease is caused by a defect in the gene for the enzyme adenosine deaminase (ADA). So in gene therapy, lymphocytes are extracted from the bone marrow of a SCID sufferer. A good copy of the human gene encoding this enzyme is introduced into these cells. This equips these cells with a good copy of the gene, in addition to the existing faulty copy. The cells thus treated are then re-injected to the patients bone marrow. |
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| Lymphocytes now produced have a fully functional ADA gene and they produce ADA to help the patients immune system. |
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