Biology Class 12 NCERT Solutions: Chapter 12 Biotechnology and Its Application Part 2 (For CBSE, ICSE, IAS, NET, NRA 2022)

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Q. 4 What are Cry proteins? Name an organism that produces it. How has man exploited this protein to his benefit?


  • Cry proteins are encoded by cry genes. These proteins are toxins, which are produced by Bacillus thuringiensis bacteria.
  • This bacterium contains these proteins in their inactive from. When the inactive toxin protein is ingested by the insect, it gets activated by the alkaline pH of the gut.
  • This results in the lysis of epithelial cell and eventually the death of the insect.
  • Therefore, man has exploited this protein to develop certain transgenic crops with insect resistance such as Bt cotton, Bt corn, etc.
Cotton, Corn Etc

Q5 What is gene therapy? Illustrate using the example of adenosine deaminase (ADA) deficiency.


  • Gene therapy is a technique for correcting a defective gene through gene manipulation.
  • It involves the delivery of a normal gene into the individual to replace the defective gene, for example, the introduction of gene for adenosine deaminase (ADA) in ADA deficient individual.
  • The adenosine deaminase enzyme is important for the normal functioning of the immune system.
  • The individual suffering from this disorder can be cured by transplantation of bone marrow cells.
  • The first step involves the extraction of lymphocyte from the patient՚s bone marrow.
  • Then, a functional gene for ADA is introduced into lymphocytes with the help of retrovirus.
  • These treated lymphocytes containing ADA gene are then introduced into the patient՚s bone marrow.
  • Thus, the gene gets activated producing functional T-lymphocytes and activating the patient՚s immune system.

Q. 6 Diagrammatically represent the experimental steps in cloning and expressing a human gene (say the gene for growth hormone) into a bacterium like E. coli?


  • DNA cloning is a method of producing multiple identical copies of specific template DNA.
  • It involves the use of a vector to carry the specific foreign DNA fragment into the host cell.
  • The mechanism of cloning and transfer of gene for growth hormone into E. coli is represented below.
Gene for Growth Hormone

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