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module:DNA: Structure and function

page:Genetic modification

As scientific understanding of DNA increases, so does the ability to copy and alter the molecule. This is called genetic engineering or genetic modification. The definition of genetic modification is 'any alteration of genetic material (DNA or RNA) of an organism by means that could not occur naturally through mating or recombination'.

The genetic techniques involved could include:

  • transferring genes from one organism to another
  • moving, deleting, modifying, or multiplying genes within a living organism
  • modifying existing genes or constructing new ones, and incorporating them into a new organism.

There are many applications for genetic modification. For example, human insulin for diabetics was previously obtained from genetically-engineered bacteria from pigs. This represented a huge advance for diabetic patients. The insulin produced by this process is not recognised by the immune system, so problems suffered by diabetic patients in the past involving development of antibodies and allergy to pig insulin (a problem in the 1980s) are now totally absent. A variety of other enzymes and chemicals are now also produced by genetically-modified bacteria.

Scientists are using genetic engineering in animals to produce improved vaccines for animal diseases, and medical compounds for humans. The term 'pharming' has been used to describe these concepts.

Crop spraying from a bi-plane. picture zoom © TopFoto

Plant modification is often concerned with improving the ability to survive in particular environments, to provide greater resistance to pests and diseases, to improve nutritional qualities, and to create immunity to certain herbicides. Genetically-engineered plants are also being used to produce compounds of use to industry.

Gene therapy is the generic term for genetic modification of humans. Some trials have taken place to introduce genes into the body which can fight specific diseases. This is specifically referred to as somatic therapy - where changes may occur to selected parts of the body, but are not passed on to the next generation. Somatic therapy does not alter the gametes.

Genetic engineering of gametes or embryos is currently not permitted. In theory, such a process could be used to remove or alter the genes which cause inherited diseases. This form of gene therapy is called germline therapy. If used, it would result in changes which could be inherited.

In theory, gene therapy could be used to correct genetic defects such as sickle cell anaemia and cystic fibrosis, but also more common diseases such as cancer and heart disease. The main barrier to this sort of therapy is actually getting the treatment gene (or 'therapeutic gene') gene into the correct cell. Cells are surrounded by fatty cell membrane, which is very resistant to large molecules such as DNA passing through it. Currently, researchers are looking at alternative modes of treatment - such as engineering viruses to cross into cells carrying therapeutic genes, so allowing gene therapy.

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