Genetic engineering is a technology of gene/DNA manipulation in lab for human welfare. It has brought revolution in all life sciences. DNA has become a molecular toy in our have. We can remove or insert any piece of DNA at a specific site in a genome. Malfunctioning genes can be cut and removed; healthy normal genes can be introduced.
Bacteria make restriction enzymes for their own defense. These enzymes cut unwanted DNA into pieces
DNA is cut by molecular scissors called ‘restriction enzymes’ or restriction endonucleases, which cut DNA by making some bases at the ends unpaired, that makes the end sticky. These are obtained from bacteria.
How is a gene transplanted?
Genes identified for specific proteins are cut and isolated in a tube from a source DNA (Fig. 17.40). Source may be humans, other mammals or plants. Source is the genetic donor. The isolated gene is first inserted into a vector. Vectors are carrier molecules for carrying the genes to a suitable host bacterium. The most commonly used vectors are plasmids. Plasmids are small circular DNA molecules present in bacteria. Plasmids are placed in a solution containing the desired gene. Imagine what will happen when an endonuclease is introduced in the same solution.
It will cut open the plasmid ring with its sticky ends exposed. The complementary sticky ends of the free gene will attach with open ends of plasmid by forming hydrogen bonds. Plasmid ring will close again. Another bacterial enzyme ligase serves as molecular glue. It will seal the ends. Now the gene has been inserted / spliced in plasmid. Plasmid becomes a recombinant DNA after incorporating / splicing another DNA.
A DNA molecule formed from DNA’s of different organisms is called recombinant DNA.
how is a gene transplanted by genetic engineering.
Now bacteria are chosen as host for cloning this gene. They are exposed to recombinant plasmids. Bacteria take the plasmid in and become recombinant microbes. The bacteria reproduce into a large number of offspring each receiving a copy of the gene. it maintains the foreign gene through multiple generations. In this way multiplication of cloning host amplify the gene. The transplanted gene starts expressing itself in the host. Bacteria make the protein specified by the foreign gene.
Application of genetic Engineering
Genetic engineering is so useful that several billion dollar industry is based on it. Pharmaceutical companies manufacture hormones, enzymes and vaccines through it. These products cannot be manufactured by any other means. Human insulin of r diabetics, human growth hormone (HGH) for dwarf children, vaccines for hepatitis B and AIDS patients, and human interferon for cancer are successfully made from bacteria.
Gene therapy is given to cure patients of hereditary disease like sickle-cell anemia and hemophilia. HbA gene is placed in bone marrow cells of sickle-cell anaemic by vector. The normal gene HbA starts forming its product and the patient becomes normal. Similarly normal gene for factor ‘Viii’ is incorporated in bone marrow of a hemophiliac.
Transgenic plants and animals are being made by introducing desired foreign genes into them. Herbicide resistant cotton, and soybean, pesticide resistant wheat, viral resistant rice and melon, fungus resistant corn, potatoes and successfully. Transgenic animals are genetically deigned to improve meat yield. Today transgenic sheep and goats are secreting human drugs in their milk. Have you heard about Nancy and Ethel?
Nancy is a sheep who secretes human ATT in her milk. ATT cures emphysema, a respiratory disease. Ethel is another sheep who secretes human factor VIII in her milk.
Versus Selective Breeding
Selective breeding is another practice to improve domesticated animals and plants. We select for breeding those individuals who have characteristics of our choice. We keep on breeding and selecting individual’s generation after generation till either we are satisfied with the product or no further improvement can be done.
Starting from a lean cow with very little milk, selective breeding was done in two directions (i) most milk (ii) most meat; one group of cattle breeders ended with large size modern beef cow with meat enough for lots of kebabs, steaks and roasts, the other group ended with modern dairy cow with lots of milk.
Hybridization and selective breeding have indeed produced a large number of improved varieties of animals and plants like Neeli-Ravi Buffalo, jersey – sahiwal cow, Dhani Ox, kajli sheep, Bital goat, teddy goat, Rahu – Thaila carp, broiler and Layer chicken, maxipak wheat and super kernel Basmati rice but it is a very slow process. It takes months and even years to raise a few generations of animals and plants (17.41, 17.42).
Genetic engineering has no match. It is a jet – speed process, because it depends on generations of bacteria that take just a few minutes or hours. Moreover the diverse applications of genetic engineering like cloning, gene therapy, finger printing, and gene libraries have absolutely no comparison. Selective breeding is out of fashion, genetic engineering is the most modern.
Fig 17.41:-Neeli is the famous breed of buffalo selected for centuries in the areas Punjab where river Sutlej flows. Ravi is the best breed of Ravi areas of Punjab. Their natural hybridization in areas of the common belt of the two rivers like Okara has resulted into famous crossbreed Neeli-Ravi.
Fig 17.42:-Rahu and Thaila are the two major carps of our rivers famous for their delicious white meat. Rahu – Thaila hybrid combines the superior taste of Rahu with larger size and faster growth rate of Thaila.