Genetic engineering and genetic modification are terms used for genetic techniques which can be used to
| � | transfer genes from one organism to another |
| � | move, delete, modify, or multiply genes within a living organism |
| � | modify existing genes or construct new genes, and incorporate them into an organism |
Genes
Living cells contain chromosomes, which are made up of genetic material called DNA. DNA is the common genetic material in all living things. The more closely related organisms are the more DNA they have in common. For example, human beings have 80%of their DNA in common with other mammals, and 99% in common with primates such as a chimpanzee. Sections of DNA involved in controlling particular features of an organism are called genes. Most genes contain the information for making a specific protein.
DNA contains four bases commonly referred to as A, T, G, and C (adenosine, thymidine, guanosine, cytosine). A section of DNA equivalent to a gene contains thousands of these bases, with their order determining the particular protein the gene codes for.
Genetic Engineering - the Process
Separating out the desired gene
Cells containing the desired gene are broken open using a chemical which dissolves the cell membrane. A chemical process separates the DNA from the other components in the "cellular soup". Restriction enzymes, chemical compounds which act like DNA scissors, are used to cut out the section of DNA corresponding to the particular gene. Restriction enzymes are found in bacteria, and are unique in their ability to cut DNA. About two hundred are now known, each recognising a particular target sequence of four to seven bases which they cut out of a DNA molecule
Transporting the gene into another cell
After restriction enzymes have cut out the piece of DNA corresponding to a gene, it is replaced into a vector. A vector is the agent which will carry the piece of DNA, the gene, into another cell. Plasmids are often used as vectors. A plasmid is a ring of DNA, capable of replicating itself, and found in bacteria. Plasmids provide bacteria with a natural method of moving genes around. They are able to enter living cells and so can cross the species barrier.
The same restriction enzyme used to separate out the gene is used to cut open a plasmid. The cut ends of the plasmid are complementary to those on the gene. The ends of the plasmid are described as "sticky ends" because they combine easily with the ends of the piece of DNA which is the gene. When the cut ends of the plasmid and the piece of DNA stick together they form a new loop of DNA containing the gene. These modified plasmids are mixed with bacteria or other cells, some of which take up the plasmids and incorporate them into their DNA.
Disabled viruses can also be used as vectors, and there are other methods of replacing a new gene into a cell which do not rely upon biological vectors. Microinjection involves injecting genetic material containing the foreign gene into the recipient cell. Electroporation and chemical poration involve creating holes in the cell membrane using a weak electric current or special chemicals. Bioballistics or projectile methods literally shoot genetic material into a cell using a microscopic type of gun.
Multiplying copies of the gene (amplification)
In order to work with the products of genetic engineering scientists need to multiply the number of copies of the DNA strand containing the replaced gene. Bacteria divide about every twenty minutes, and their DNA (including the replaced gene) replicates every time the cell divides. This natural replication process can lead to billions of copies of the gene being produced in a matter of hours.
Plasmids and bacteria are still in use but most amplification of DNA is now done by an automated process called polymerase chain reaction (PCR). This process is capable of rapidly amplifying a DNA molecule into many billions of molecules in a cell-free environment.
Uses of Genetic Engineering
Human insulin has been produced by genetically-engineered bacteria since the 1980s. Insulin is a protein normally produced by the pancreas in humans. People with diabetes cannot produce insulin, which means that they cannot process glucose. Insulin for diabetics was obtained from pigs until the 1980s, when genetically-engineered bacteria became the means of producing high quality insulin. The piece of DNA (the insulin gene) which codes for the production of insulin is replaced into Escherichia coli, a bacterium found in the human stomach. The normal multiplication processes of the bacteria produce billions of copies of the human insulin gene, which allows the modified bacteria to produce quantities of insulin. This is then extracted and purified for use by diabetics.
Human interferon and growth hormone are being produced by the same method. A variety of other enzymes and chemicals are now also produced by genetically-modified bacteria.
Gene therapy
Gene therapy is the name given to genetic modification of humans. Some trials have taken place to introduce genes which are able to fight a particular disease into the body. This is called somatic therapy, and it changes selected parts of the body. The changes to the DNA in the person are not passed on to the next generation, because they do not alter the gametes (eggs and sperm). Genetic engineering of gametes or embryos is currently not permitted, but could in theory be used to remove or alter the genes which cause inherited diseases. This form of gene therapy is called germ-line therapy, and if used would result in changes which could be inherited. Scientists are using genetic engineering in animals to produce improved vaccines for animal diseases, and medical compounds for humans (pharming). Plants are being modified to improve their ability to survive in particular environments, to provide greater resistance to pests and diseases, to improve nutritional qualities, and to give immunity to certain herbicides. GE plants are also being used to produce compounds of use to industry.
There are both risks and benefits in the use of genetic engineering. Some groups, such as organic farmers, are fundamentally opposed to the use of this technology, and other groups have concerns about food and environmental issues.
In New Zealand the Environmental Risk Management Authority (ERMA) makes decisions on the development and importation of genetically-modified organisms. In June 2000 the Royal Commission on Genetic Modification was established and carried out a year-long inquiry into the strategic options available to enable New Zealand to address genetic modification now and in the future. The Commission's Report was published in mid-2001, and proposed that New Zealand should follow a "proceed with caution" approach to genetic modification.
In response to key points in the Royal Commission's report, the New Zealand Government put a moratorium on field trials of genetically modified organisms in place for two years to allow for further research into safety and environmental issues. That moratorium was allowed to expire in October 2003 with the passing of the New Organisms and Other Matters Act. This Act modified the Hazardous Substances and New Organisms Act which provides the regulatory framework for the work of the Environmental risk Management Authority.
New Zealand Catholic Bishops submission to the Royal Commission on Genetic Modification
The Nathaniel Centre Comment on the Report of the Royal Commission on Genetic Modification
New Zealand Government response to the Royal Commission's Report