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Crystals of Bt toxin produced by some bacteria do not kill the bacteria themselves because

  • bacteria are resistant to the toxin
  • toxin is immature
  •  toxin is inactive
  • bacteria encloses toxin in a special sac


 toxin is inactive

What is gene therapy? Illustrate using the example of adenosine deaminase (ADA) deficiency.

Gene Therapy. It is defined as the introduction of a normal functional gene into cells which contain the defective allele of concerned gene with the objective of correcting a genetic disorder or an acquired disorder.

Treatment of ADA deficiency. 1. Gene therapy was used to correct the genetic disorder called Severe Combined Immuno Deficiency (SCID) syndrome produced by adenosine deaminase (ADA) deficiency.

2. In this, Normal ADA gene copies were produced by cloning.

3. Packed into defective retrovirus, most of the viral genes were replaced by ADA gene.

4. Lymphocytes were isolated from the patients.

5. Recombinant DNA of the recombinant retroviruses were used to infect the lymphocytes.

6. The infected cells expressing the ADA gene were injected back into the patients.

7. The normal ADA gene was then expressed in the patients and ADA deficiency is partially corrected. If the gene isolated from bonemarrous cells producing ADO is introduced into embryonic cells at early stages, it could provides permanent cure.

Steps involved in gene transfer for the production of growth hormone

Steps involved in gene transfer for the production of growth hormone


Compare and Contrast the advantages and disadvantages of production of genetically modified crops.

Advantages and Disadvatages of Genetically modified (GM) Crops.

Advatages Disadvantages
1. GM crops are developed for pest resistance and thus  the yield increases and there is less dependence on pesticides.                   1. GM crops that show pest resistance prove harmful for pollinators and hence pollination.
2. GM crops are developed to increase the nutritional value in the crops. 2. GM crops can lead to severe allergies in some and may not be as good in taste as the natural crop.
3. They can be used  to develop crops  which are more tolerant to abiotic stresses 3. The pollen of GM crops is also modified and can lead to the development of resistance and growth of  super-weeds. Weeds prove harmful to the environment and crops.  
4. GM crops can be developed to have antibiotic properties                   The intake of GM crops having antibiotic properties may lead to antibiotic resistance in some and less efficacy of antibiotic medications.
5. GM crops can be modified to benefit humans.  5. The patent provided for the development of GM crops  has been creating problems because the companies are benefited while the farmers are at loss.


What are transgenic bacteria ? Illustrate using any one example.

Transgenic bacteria are those bacteria whose DNA is manipulated to possess and express an extra (foreign) gene .

Example. Transgenic bacteria like E.coli which produces insulin. This bacteria is genetically manipulated by introducing two DNA sequences corresponding to A and B chains of human insulin in plasmids of E. coli to produce insulin chains. Chains A and B produced separately are extracted and  combined by disulfide bonds to form human insulin.


What are Cry proteins? Name an organism that produce it. How has man exploited this protein to his benefit?

Cry proteins are crytalline proteins that are toxic and insecticidal in nature.

They are produced by bacteria called  Bacillus thuringiensis. The toxic protein is present in active form in bacteria which when ingested by an  insect leads to the activation of protein and subsequent death of insect.

Man has benefited from this protein by incorporating the Bt-toxin gene that produces the Cry protein in several crop plants like cotton. The incorporation of gene in plants makes them insect resistant and thus help in good yield and productivity.