Principles of Methods of Genetic Modified Food

There are various techniques used to genetically modify foods. Food may be genetically modified to increase its shelf life, make it resistant to pesticides and insecticides, or improve the crop nutritional yield.Genes use chemical messages that instruct the cell to perform its functions by making proteins or enzymes. By introducing a foreign gene, the altered organism make new proteins or enzymes so that the cell performs new functions. For example, the gene that helps a coldwater fish survive low temperatures can be inserted into a strawberry to make it frost-resistant. The genes can be taken from an animal, plant or micro-organism. If the genes are inserted into another species, the resulting organism is referred to as transgenic.

Bacterial carriers
The natural ability of the bacterium Agrobacterium tumefaciens is the principal technique for genetic modification of plants. This bacterium can infect plants, which makes it a suitable carrier for delivering DNA.

The selected gene is inserted into the bacterium plasmid (a circular piece of DNA) and dropped into a special solution, which is able to make the cells of the bacterium more porous. The solution is then heated, which allows the plasmid to enter the bacterium and express the new genes. Crown gall, a tumor-like growth is resulted when the plant is infected with this bacterium. The ‘recombinant’ (genetically altered bacterium) is allowed to rest and grow. Depending on the plasmid, it may develop extra copies of the new gene. The bacterium is then allowed to infect the target plant so it can deliver the plasmid and the new gene.Inserting additional genes of interest into A. tumefaciens and transfer those genes into plants is commonly used to create transgenic crop plants for agricultural purposes.

Bioloistics
Biolistic method (gene gun), is another widely used process to create transgenic crops. It is a method used for the creation of the two most common transgenic crops –Roundup Ready soybean and Bt-corn. It involves shooting new genes into the potential host. The selected DNA is attached to microscopic particles of gold or the metal tungsten. Like firing a gun, these DNA-laden particles are shot into the target cells using a burst of gas under pressure.

Electroporation
The prepared target cells, together with the selected DNA are immersed in a special solution in electroporation. A short but intense electric shock is then passed through the solution. This results in small tears in the cell walls, which allows the new genetic material access to the nuclei. Aftermath, the cells are placed into another solution and encouraged to repair their breached walls, locking the DNA inside the cell. The selected DNA is incorporated into the host chromosomes to provide the host with a new gene.

Gene silencing
Gene silencing is used to prevent plants like peanuts and wheat from producing the proteins (allergens) that often cause allergies to humans. The gene that is responsible for the undesirable trait is identified. One method to ‘silence’ that particular gene is to attach a second copy of the gene the wrong way round.

Gene splicing
Genetic modification involves genetic engineering, which is also known as gene splicing. It is a technique to splice together DNA fragments from more than one organism. Thus, this prepares a ‘recombinant’ DNA molecule in a test tube, producing a single piece of genetic material containing the original information from multiple fragments which can then be inserted into another organism. This is achieved by cutting up DNA molecules with restriction enzymes and joining these fragments together using DNA ligase. Generally, there are two classifications of genetic modification; modifying of plants and animals.

Viral carriers
Like bacteria and plants, animals can also be genetically modified by viral infection. A virus that will invade the target cells but not cause damage or death is chosen. The selected DNA is thus added to the genetic makeup of the viurs, and then the virus is allowed to infect the target. As the viurs invades the cells and replicates, the selected DNA is added to the target cells.

Lipofection
Lipofection is a method using small bubbles of fat called liposomes as the carriers of selected DNA. The target cells and the liposomes are placed into a special solution. When the liposomes merged with the cell membrane, it allows the DNA to enter the cells for inclusion in the chromosome.

Microinjection
Injection is a method primarily used in animals. The new DNA is injected into the nucleus of a fertilised egg which can then be placed back in the female uterus where the injected cell is allowed to develop normally. Unfortunately, there is a high rate of failure when using this technique as the cells take up and express the desired traits of the introduced DNA infrequently.For microinjection, the selected DNA is injected into a fertilised ovum through a glass capillary tube. The genetically modified egg is then transplanted into the prepared uterus of a receptive female and is allowed to grow to term.

Microinjection is common way to create transgenic fish. Mosaic is the first generation but several lines have been produced with the transgene incorporated into the germ line and transgenic fish can then be produced naturally by crossing male and female gametes.

Although many types of transgenic fish exists (e.g. for increased cold tolerance, antibiotic production, ornamental Glofish etc), the main focus had been on so called growth hormone transgenic fish, mainly salmonids, tilapias and carps. These fish have an over-production of growth hormone which results in an increased growth rate of 30-40 times that of wild-types. The final size of some species is increased as well as the growth rate, providing an incentive for commercial breeders to farm such fish. However, for ecological concerns, potential negative effects of transgenic fish in nature largely prevent the commencement of commercial production.

Protoplast transformation
Protoplast transformation is commonly used in plants. The cellulose in the plant cell wall is dissolved away using enzymes leaving a protoplast. DNA can then be inserted to the protoplast which are then cultured on a growth media. This encourages the protoplast to regrow the cell walls and thus eventually grow into a transgenic plant.