Genetically modified organisms are the species which have a foreign gene in their DNA. This gene shows certain traits which scientists want to see in an organism. Usually Recombinant DNA technology is used to make an organism genetically modified. Like animals, plants have also been made genetically modified so that they can show resistance against diseases and insects which damage their function and production.
There are certain methods through which the organism can have alterations in their genetic makeup.

Human and Animal Cell as a Host:-
When the process of trangenesis in animals is concerned, the method of DNA microinjection is used. This method involves insertion of foreign gene into the nucleus of fertilized ovum. It is not the matter of certainty that whether this gene will express itself or not until the transgenic animals are mated. This will show whether the desired gene has been transferred into the next generation or not.

Another method for the transfer of foreign gene into animal cell is embryonic stem cell mediated gene transfer also used. In this method, the gene of interest is inserted into the embryonic stem cells which are then introduced into the embryo.

Retrovirus mediated gene transfer is another method. As retroviruses are able to transfer their genome into the host cell to cause infection that is why they have been used to transfer the desired gene into the animal body. In this process, the activity of the retrovirus is blocked and they can only transfer the gene of interest. In this method, all the cells of the animal do not get the foreign gene and the animal will be called as chimeric animal. The gene of interest will only transmit in the entire cell if the retrovirus injects it into the sex cells of the organism otherwise the chimeric organism will have to produce 20 generations until the desired gene spreads in all the cells.

Transgenic animals are currently being used to produce milk with human growth hormones and insulin, pigs which can produce human organs and sheep. Monoclonal antibodies can also be produced from genetically modified organisms.

Plant cell as a Host:-
To insert the foreign gene into the plant cell, agrobacterium tumefaciens are used as vectors. They carry the gene of interest and insert it into plant cell in the way as they usually infect their own genetic material into plant cell. By cutting the small part of plasmid wit restriction enzymes and inserting the desired gene with ligase into the plasmid, it is injected into the desired plant cell. Mostly produced plants through this method are Bt corn and Bt cotton which contain the gene of bacillus thuringiensis which make the plant toxic and insects cannot attack the plant otherwise they will die if they attacked. Genetically modified soybeans are also produced through this method. If the genes are inserted into cereals or grasses, it is more difficult because they don't have proper root system. For example, genetically modified canola, sugar cane and corn are the examples of monocotyledonous plants.

Bacterial Cell as a Host:-
Bacteria start the process of transformation when it has a plasmid in its cell. Plasmid is the circular DNA which contains foreign gene. When the plasmid is inserted inside the bacterium, it will start replicating along with the bacterial genome and all the bacterial generations will have the gene which was inserted through plasmid. Recombinant DNA technology is used for this purpose in which restriction enzymes cut the desired gene from the DNA of human cell and insert it into plasmid by cutting a small portion of its circle and attaching the foreign gene with its genetic material by using an enzyme called ligase. This plasmid will be inserted into the bacterial cell and after replication multiple copies will produce along with the bacteria's own genetic material. The resulting recombinant bacteria can be used for various purposes in the field of science for example, medicine, research and pharmaceuticals for the production of human growth hormones, insulin and for the drug delivery.

Ethical and Environmental Issues:-
Critics believe that genetically modified crops and organisms are the cause of genetic pollution as genes can be transferred from related to unrelated species where genetic alteration is not needed. Herbicide resistance can transfer into weeds which cannot be eradicated through herbicides. GM organisms may be the source of transferring their genes into wild species which is not needed. For example, a genetically modified organism like Sumo Salmon fish contains the human growth hormone gene.

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