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Biology · 2025 · 5 marks
Biotechnology : Principles and ProcessesProcesses of Recombinant DNA Technology5 marksUnderstandlong answer
CBSE 2025 · Region 4 · Set 2 · Q33
(a) (i) Name the two genes encoding for the Bt toxin protein used in biotechnology for the control of cotton bollworms. (ii) How does the expression…
(a)(i)
Name the two genes encoding for the Bt toxin protein used in biotechnology for the control of cotton bollworms.
(ii)
How does the expression of Bt toxin gene in Bt cotton plant help in providing resistance to cotton bollworms ? Explain.
OR
(b)(i)
Explain the given methods of introducing the alien DNA in the host cells :
(I)
Biolistics
(II)
Microinjection
(ii)
How is E. coli made 'competent' to take up a recombinant plasmid or DNA ?
Marking-scheme solution
(i)
cryIAc and cryIIAb.
(ii)
Bt toxin is coded by a gene cry , on expression the gene toxic insecticidal protein crystals are formed , which remain in inactive protoxin form , but once an insect ingests the inactive toxin it becomes active , due to the alkaline pH of the gut , it solubilises the crystals , and binds to the surface of epithelial cells of midgut and create pores swelling and lysis , and eventually cause death of the insect.
(i)
(I)
In biolistics cells are bombarded with high velocity
micro-particles of gold or tungsten coated with DNA, into plant cells
(II)
In microinjections recombinant DNA is injected directly
into the nucleus of, animal cell.
(ii)
E. coli is treated with a specific concentration of a divalent cation such as calcium, this creates (temporary) pores in the cell wall of bacterium which facilitates entry of plasmid or rDNA into the bacterium.
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CBSE Class 12 Biology past-paper question from the 2025 board exam, with the answer as CBSE’s own marking scheme gives it. Where our answers come from.