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What is Gene Transfer?

Gene transfer is a technique where new DNA is added to the cells of a living organism. This can be done by using carriers like plasmids or modified viruses. The new DNA can be added to the cells outside the organism and then put back into the organism, or it can be directly added to the cells inside the organism.  

Types of Gene TransferTypes of Gene Transfer

Steps involved in Gene Transfer

The process of gene transfer can be summarized in four key steps:

(a) Isolation of gene and vector (by PCR)

(b) Digestion of gene and vector (by restriction endonuclease)

(c) Ligation of gene and vector (by DNA ligase)

(d) Selection and expression of transgenic construct

Methods for Gene Transfer

There are two methods of gene transfer:

(a)  Indirect or Vector-Mediated Gene Transfer

Indirect or vector-mediated gene transfer in plants involves the use of a plasmid vector.  One widely employed vector for plant transformation is the Ti-plasmid found in Agrobacterium tumefaciens. 

Agrobacterium-mediated Gene TransferAgrobacterium-mediated Gene Transfer

  • This bacterium carries a relatively large plasmid called the Ti plasmid (which stands for Tumor-inducing plasmid). A specific portion of this plasmid, known as T-DNA (Transfer DNA), is integrated into the plant genome within infected cells, leading to the development of plant tumors, or crown galls. 
  • Due to its inherent ability to naturally transfer the T-DNA region from its plasmid into the plant genome upon infecting wounded plant cells, Agrobacterium tumefaciens is often referred to as nature's genetic engineer for plants.
  • The foreign gene (e.g. Bt gene for insect resistance) and plant selection marker gene, usually an antibiotic gene like npt II which confers resistance to antibiotic kanamycin are cloned in the T DNA region of Ti-plasmid in place of unwanted DNA sequences.

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(b) Direct or vectorless gene transfer method.

In the direct gene transfer methods, the foreign gene of interest is delivered into the host plant without the help of a vector. The following are some of the common methods of direct gene transfer in plants.

The various method of direct gene transfer is: 

(i) Chemical method
Use chemicals like polyethylene glycol and polyvinyl alcohol to help plant cells take in foreign DNA.
Start with plant protoplasts (cells without cell walls) in a magnesium-rich medium.
Add plasmid DNA with the desired gene. Use polyethylene glycol, maintain pH at 8, and briefly heat protoplasts. Cool them on ice to boost DNA uptake.
Allow incubation for DNA integration. Later, reduce polyethylene glycol and increase calcium ions for better transformation efficiency.

(ii) Electroporation
 A pulse of high voltage is applied to protoplasts, cells or tissues which makes transient pores in the plasma membrane through which uptake of foreign DNA occurs.
Genetic Engineering Technique: Gene Transfer | Science & Technology for UPSC CSE 

(iii) Biolistic gun
Foreign DNA is attached to tiny gold or tungsten particles, typically measuring 1-3 µm. These particles are then shot onto the target tissue or cells using a device known as a gene gun, micro projectile gun, or shotgun. After bombardment, the treated cells or tissues are grown in a specific medium to encourage the development of plants from the modified cells.
Gene GunGene Gun

(iv) Microinjection

The DNA is directly injected into the nucleus using fine tipped glass needle or micro pipette to transform plant cells. The protoplasts are immobilised on a solid support (agarose on a microscopic slide) or held with a holding pipette under suction. 

MicroinjectionMicroinjection

(v) Lipofection

Artificial phospholipid vesicles called liposomes are valuable for transferring genes. They enable the transfer of genes or DNA from the liposome into the vacuole of a plant.

Achievements of Genetic Engineering

DNA recombinant technology or genetic engineering provides great benefits for the advancement of science and society.

1. Gene Therapy: 

A new system of medicine gene therapy, may develop to treat hereditary diseases such as haemophilia. – It is the technique for curing genetic disease by replacing a "Faulty Gene" with a normal healthy functional gene.

  • The first gene therapy used in severe combined immunodeficiency (SCID) patient.
  • About 25% of an infant with SCID disorder lack the enzyme adenosine deaminase (ADA) – ADA enzyme involved in purine metabolism.
  • These patients have no functioning T & B lymphocytes.
  • The affected child of SCID develops recurrent infection early in life because they have no immune response against invading pathogen.
  • The ideal approach would be to give the patient a functioning ADA by gene therapy.
  • Thus, the genetic disorder can be overcome by introducing a specific gene.

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2. Bacteria 

as "Living factories" for synthesizing vitamins, hormones and antibodies.

  • Human insulin (Humulin) was the first genetically engineered product produced by an American firm Eli Lilly – 5th July 1983.
  • Charles Weismann of the University of Zurich obtained interferon through recombinant E.coli (1980).
  • Microbes have been engineered to produce Human Growth Hormone (HGH) for curing dwarfism.
  • Vaccines are produced by genetic engineering e.g., for Hepatitis-B and Herpes virus).
  • Nitrogen fixation genes may be transferred from bacteria to the major food crops to boost food production without using expensive fertilizers.
  • Transgenic plant obtained through recombinant DNA technology. The first transgenic plant was tobacco.

TobaccoTobacco

  • It contains a resistant gene against weedicide (Glycophosate).
  • The first transgenic animal was a mouse contain the gene for growth hormone.
  • The first introduced transgenic crop in India (2002) is Bt-cotton.
  • It is resistant for boll worm (Helicoverpa armigera - Larva of insect). 
  • It is formed by the transfer of a pest-resistant gene from Bacillus thuringiensis (bt-2 gene encoding Bt–toxin).
  • Bacillus thuringiensis produces a toxic protein called crystal protein (Cry-Protein) this protein is toxic for the larva of a certain insect.

Cry-proteinCry-protein

  • This protein kills the insect by inhibiting ion transport in the mid-gut (bt 2 genes is called cry -gene) – In pollution control, microbes have been engineered to break up the crude oil spills.
  • Dr Ananda Mohan Chakraborty introduced plasmid from different strains into a single cell of pseudomonas putida. The result was a new genetically engineered bacterium that would clean oil spills called "Superbug" (oil eating bug.)

3. Medical Diagnosis of Disease 

  • Recombinant DNA technology is one of the important tools for the diagnosis of several diseases. The diagnostic technique involves the construction of probes consisting of short segments of single-stranded DNA attached to a radioactive or fluorescent marker.
  • Such probes are used to identify infections agents such as Salmonella (cause food poisoning), Staphylococcus (pus-forming bacterium), hepatitis virus, HIV; muscular dystrophy, cystic fibrosis and so on. 
  • Recombinant DNA technology can also be employed to predict the inheritance of genetic disorders from carrier parents. The chances of birth of an affected child can be predicted by testing the DNA of repetitive prospective genetic disorder carrier parents.

Question for Genetic Engineering Technique: Gene Transfer
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Which method of direct gene transfer involves the use of chemicals to help plant cells take in foreign DNA?
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Application

 of Recombinant DNA Products


Application of Genetically Engineered Microbes
Genetic Engineering Technique: Gene Transfer | Science & Technology for UPSC CSE

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FAQs on Genetic Engineering Technique: Gene Transfer - Science & Technology for UPSC CSE

1. What is gene transfer?
Gene transfer refers to the process by which genetic material is transferred from one organism to another. It involves the introduction of specific genes or DNA sequences into the genome of the target organism, thereby altering its genetic composition.
2. What are the steps involved in gene transfer?
The steps involved in gene transfer typically include: 1. Isolation of the desired gene: The gene of interest is identified and isolated from the source organism's DNA. 2. Cloning of the gene: The isolated gene is amplified through the process of DNA cloning, producing multiple copies of the gene. 3. Insertion of the gene into a vector: The gene is inserted into a carrier molecule called a vector, such as a plasmid or a virus, which is capable of delivering the gene into the target organism's cells. 4. Transformation of the host organism: The vector containing the desired gene is introduced into the target organism's cells, enabling the transfer of the gene into the host's genome. 5. Expression of the gene: Once the gene is integrated into the host genome, it can be transcribed and translated, leading to the production of the desired protein or alteration of the target organism's traits.
3. What are the methods for gene transfer?
There are several methods for gene transfer, including: 1. Electroporation: In this method, a brief electric pulse is applied to the target cells, creating temporary pores in their membranes. This allows the DNA to enter the cells. 2. Microinjection: This technique involves the direct injection of DNA into the nucleus of the target cells using a fine glass needle. 3. Viral vectors: Viruses are genetically engineered to carry the desired gene and infect the target cells, transferring the gene into the host genome. 4. Lipid-mediated transfection: Lipid-based molecules are used to encapsulate DNA and facilitate its entry into the target cells. 5. Gene gun: This method involves coating tiny metal particles with DNA and shooting them into the target cells using a high-pressure burst of gas.
4. What are some achievements of genetic engineering through gene transfer?
Genetic engineering through gene transfer has led to several significant achievements, including: 1. Production of recombinant proteins: Gene transfer has allowed the production of valuable proteins, such as insulin and human growth hormone, in large quantities using genetically modified organisms. 2. Crop improvement: Genes can be transferred into crop plants to enhance their nutritional value, increase resistance to pests and diseases, and improve tolerance to environmental stresses. 3. Gene therapy: Gene transfer techniques have paved the way for the development of gene therapy, which aims to treat genetic disorders by introducing functional genes into patients' cells. 4. Creation of genetically modified organisms (GMOs): Gene transfer has enabled the creation of GMOs with desired traits, such as herbicide resistance or increased crop yield. 5. Development of vaccines: Genetic engineering has facilitated the production of vaccines by introducing genes encoding viral or bacterial antigens into host cells, leading to the production of specific immune responses.
5. What is the significance of gene transfer in the field of medicine?
Gene transfer plays a crucial role in the field of medicine as it has the potential to revolutionize disease treatment and prevention. Some of its significances include: 1. Gene therapy: Gene transfer techniques allow the introduction of functional genes into patients' cells, offering potential treatments for genetic disorders, cancers, and other diseases. 2. Drug development: Gene transfer can be utilized to create animal models with specific genetic modifications, aiding in the development and testing of new drugs. 3. Vaccine production: Genetic engineering enables the production of vaccines by introducing genes encoding viral or bacterial antigens into host cells, leading to the production of specific immune responses. 4. Tissue regeneration: Gene transfer can be used to deliver genes that promote tissue regeneration and repair, offering potential solutions for treating injuries and degenerative diseases. 5. Personalized medicine: Gene transfer techniques can be employed to create personalized treatments based on an individual's genetic makeup, allowing for more targeted and effective therapies.
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