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Overview Of Genetically Modified Organisms (Gmos), Its Features, Applications, Advantages And Disadvantages

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Definition:

GMO is an organism whose genetic makeup is modified or changed, not by mutation or accidental cross-breeding, but by using latest bio-techniques like Recombinant DNA technique, in which different genetic materials are combined. This process of modification is called Genetic Modification OR Genetic engineering. This step is taken to make organisms more useful and adaptable.

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Description:

Genetic Engineering of organisms involved in it, by changing the genome of organisms using mostly, recombinant DNA technique. In which desired traits and characteristics are taken by removing and inserting genes of interests. Genes of interest are taken from any other species of organism having that desired characteristics.

History:

Generally, GMOs are under the results of genetic engineering. It has been going on for very long time by the name of “Selective Breeding” Artificial Selection and other common methods results from hairless cats to sweet corn and human like versions of mice gene FOXP2.

The alternation of genetic material by insertion or removal was made possible after the discovery of Recombinant DNA Bactrian in 1973.

E-coli were this bacterium first ever genetically modified by great scientist HERB BOYER and STANELY COHEN. In 1978, Genentech (Biotechnology Corporation founded by venture capitalist Robert A. Swanson and biochemist Dr. Herbert Boyer. in 1976) announced that E. coli’s one strain can produce human insulin.

Glofish was first GMO animal sold as pet. Since 1996, Genetically Modified foods and crops are being cultivating rapidly.

Now-a-days, there is a huge diversity in G. M. Os as food, animals, agriculture and medicine.

What are not Genetically Modified Organisms?

These do not include organisms whose modification is due to:

  • Fusion of animal cells unless the product can form an animal.
  • Plants formed X-protoplast fusion.
  • Plants formed by embryo rescue or in vitro fertilization.
  • Formed by zygote implantation.
  • Organisms formed by natural DNA transfer.

Techniques Used For Genetic Modification:

There are many techniques used in genetic modification or engineering Following are the most commonly used techniques in Genetic Modification.

  1. Recombinant DNA Technology
  2. Bioballistics Method
  3. Electro and Chemical proration
  4. Microinjection

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1. Recombinant DNA Technology:

To cut a gene of interest from one organism and insert to other organism to get the benefit of that gene of interest. Following are the steps involved in Recombinant DNA techniques:

  1. Isolation of Gene of interest.
  2. Piece of DNA is cut with a restriction enzyme and then ligate the DNA insert into the vector(on which the gene of interest is placed) with DNA Ligase enzyme.
  3. Now, the gene or DNA along with the vector is called recombinant DNA is produced, and is introduced into an expression system as a result of which specific result or product is obtained.

Explanation of the Complete Process:

Following are the steps in rDNA process.

1. Isolation of gene of interest:

In rDNA is the isolation or getting of gene of interest. Three possible ways to get the gene of interest

A. To isolate it from the Chromosomes:

Gene can be isolated from the chromosomes by cutting the chromosomes and getting genes using special enzymes Known as restriction Endonucleases.

Restriction Endonuclease:

An enzyme which cuts the double stranded DNA is known as restriction endonuclease or restriction enzyme.

Structure of Restriction Endonuclease

Such enzymes, found in archaea and bacteria, are thought to have evolved to provide a defense mechanism against invading viruses. Inside a bacterial host, the restriction enzymes selectively cut up foreign DNA but does not harm to bacterial chromosome. In 1970,Hamilton O. smith,at Johns Hopkins University isolated the first restriction enzyme.

These enzymes cut the DNA at very specific sites(known as restriction sites) characterized by specific sequence of four or six nucleotides symmetrically in the reverse order. Thes sequences are called Palindromic sequences. In fig. below AATT (5′-3′ ) and TTAA (3′-5′ ) are palindromic sequences.

Palindromic sequence

When it cuts DNA sticky ends are created from palindromic sequences.

Restriction enzyme EcoR1 ,cuts specific sequence of nucleotides in such a way that sticky ends are produced

There are more than 400 such enzymes have been isolated and out of these 20 are frequently used in recombinant technology. Most commonly used restriction enzyme is EcoR1(isolated from strains of E. coli).

EcoRI crystal structure

EcoRI recognition site with cutting pattern indicated by a line

Some other restriction enzymes are: EcoRII (isolated from Escherichia coli) , BamHI (isolated from Bacillus amyloliquefaciens), TaqI(isolated from Thermus aquaticus).

B. To synthesize it chemically

If genes are small they can be synthesized in the laboratory

C. To make it from mRNA:

This is another method used for getting gene of interest. Using messenger RNA by reverse transcriptase. This DNA molecule is called complementary DNA.

2. Selection of Vector:

A vector is a DNA molecule used as a vehicle to transfer foreign genetic material into another cell.

Selection of a vector is also important step to make the recombinant DNA. Means by which rDNA is introduced into host cell. Two types of vectors are commonly used in recombinant DNA technology ,

  1. Plasmid
  2. Viruses
  3. Recombinant DNA:

Recombinaanat DNA is DNA which have foreign piece of DNA is present. For the preparation r DNA ,the plasmid is cut with the same restriction enzyme which was used for isolation of the gene of interest the of interest is then joined with sticky ends produced after the cutting of the plasmid with the help of an enzyme DNA ligase. This enzyme seals the foreign piece of DNA into vector Now the two different pieces of DNA have been joined together ,which is known as recombinant DNA or chimaeric DNA.

Types Of Recombinant DNA Technique

On the basis of the usage of vector there are two types of rDNA technology are:

1. Vector method:

In this method viral DNA is used as vector,its product is directly inserted into the genome via a viral chromosome.

2. Plasmid method:

Plasmid is a DNA molecule that and can replicate independently. These are double-stranded and, in many cases, circular. Plasmids usually occur naturally in bacteria, Plasmids were discovered by investigators studying the sex life of the intestinal bacterium Escherichia coli. Plasmid are natural extra chromosomal circular DNA.

Bacterial cell plasmid inside the cell

In this method plasmid is used as vector to carry gene of interest. and this can be implemented the gene into plants and animals.

Schematic Diagram of plasmid method is shown below

Applications of Recombinant DNA technology Method

Recombinant DNA is widely used in biotechnology, medicine and research. The most common application of recombinant DNA is in basic research, where it is important to most current work in the biological and biomedical sciences. Recombinant DNA is used to identify, map and sequence genes, and to determine their function.

Many additional practical applications of recombinant DNA are as:

1. Recombinant human insulin.

Recombinant insulin has almost completely replaced insulin obtained from animal sources (e. g. pigs and cattle) for the treatment of insulin-dependent diabetes. A variety of different recombinant insulin preparations are in widespread use.

2. Recombinant blood clotting factor VIII.

Recombinant factor VIII is a blood-clotting protein that is administered to patients with forms of the bleeding disorder hemophilia, who are unable to produce factor VIII in quantities sufficient to support normal blood coagulation

3. Golden rice:

golden rice is a recombinant variety of rice that has been engineered to express enzymes responsible for β-carotene biosynthesis. This variety of rice holds substantial promise for reducing the incidence of vitamin A deficiency in world’s population.

4. Herbicide Resistant Crops:

Varieties of important agricultural crops (including soy, maize/corn, sorghum, canola, alfalfa and cotton) have been developed which incorporate a recombinant gene that results in resistance to the herbicide glyphosate and simplifies weed control by glyphosate application. These crops are in common commercial use in several countries.

5. Insect-resistant crops.

Bacillus thuringeiensis is a bacterium that naturally produces a protein (Bt toxin) with insecticidal properties. The bacterium has been applied to crops as an insect-control strategy for many years, and this practice has been widely adopted in agriculture and gardening. Recently, plants have been developed which express a recombinant form of the bacterial protein, which may effectively control some insect predators. Environmental issues associated with the use of these transgenic crops have not been fully resolved

2. Bioballistic Method:

This is also called micro-projectile bombardment or gene gun or biolistics. This technique is used for in vivo, within a living organism, transformation and has been especially useful in transforming monocot species like corn and rice. This approach literally shoots genes into plant cells and plant cell chloroplasts. DNA is coated onto small particles of gold or tungsten approximately two microns in diameter. This technique can also be used for RNA, if desired. The particles are placed in a vacuum chamber and the plant tissue to be The Helios Gene Gun by BioRad engineered is placed below the chamber. The particles are propelled at high velocity using a short pulse of high pressure Helium gas into any target cell or tissue.

Gene Gun used for Bioballistics

The biolistic method is most useful for inserting genes into plant cells such as pesticide or herbicide resistance. Different methods have been used to accelerate the particles: these include pneumatic devices; instruments utilizing a mechanical impulse or macroprojectile; centripetal, magnetic or electrostatic forces; spray or vaccination guns; and apparatus based on acceleration by shock wave, such as electric discharge.

Helios Gene Gun schematic

3. Electro and Chemical proration:

In this method,the targt cell and selected DNA are placed in a special solution and electric shock is passed through solution which causes pores in target cells and DNA goes inside the cell. This is done in an instrument called electroporator. Special chemicals, such as polyethylene glycol, are also used to make pores in cell surface. Then cells are placed in another solution & allow to repair their cell walls. thus locking new DNA. Selected DNA incorporates into host chromosomes.

4. Microinjection:

The process in which a glass micropipette is used to insert substances at a microscopic level into a single living cell. It is a simple mechanical process in which a needle roughly 0. 5 to 5 micrometers in diameter penetrates the cell membrane and the nuclear envelope. The desired genes are then injected into the desired sub-cellular compartment and the needle is removed. The injected genes are automatically enter into the nucleus where they incorporate with the host cell’s genetic material and replicate with it.

Advantage and Disadvantage

Advantages of GMO:

  1. 1. GMO have more resistance for diseases and the widespread plant diseases cannot spread in GMO widely
  2. 2. Unexpected frost usually destroys sensitive seedlings. To make plants tolerant from unexpected frost, an anti-freeze gene from cold water fishes has been introduced into plants such as tobacco and potato
  3. 3. GMO are more droughts tolerant. Theses can withstand long periods of drought or high salt content in soil, and water. Farmers can grow crops in unsuited places, due to GMO.
  4. 4. GMO foods have high nutrition. The nutrients that are not naturally present in some foods are inoculated in them using Genetic Modification. E. g. rice
  5. 5. Scientists are working to develop edible and less costly vaccines for third world countries. They are working on tomatoes and potatoes.
  6. 6. Plants are Genetically Modified to have greater tolerance against the herbicidic sprays. So that the herbs will die but plants will withstand against the spray of herbicides to remove herbs. This improves the quality of plant products.
  7. 7. Plants are genetically modified to be resist against the harms of different kinds of pests.
31 October 2020

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