Q20 of 26 Page 1

Biotechnology has helped farmers to get pest resistant cotton crops. Explain the technique adopted along with its mode of action. (Mention six points)

OR


Draw the figure of vector pBR322 and label the following: Origin of replication, Ampicillin resistance site, Tetracycline resistance site, Bam H1 restriction site.


1. Biotechnology has helped farmers to get pest resistant cotton crops. The technique adopted is the bio pesticide ‘Bt toxin’, produced by the bacteria Bacillus thuriengiensis.


2. The genes of this toxin, also known as Cry genes, encode the toxin.


3. Specifically Cry I Ac and Cry II Ab encode the proteins which kills the pest in the cotton bollworm. This toxin is incorporated into the crop.


4. Whenever this Bt toxin is ingested by the insect, it is converted into the active form due to the alkaline pH of the insect’s gut.


5. The activated form of the toxin binds with the surface of the epithelial cells of the gut.


6. This binding of the toxin with the surface of the epithelial cells of the gut, makes pore in the cells causing them to swell thereby killing these cells.


OR


Site of origin:


1. Origin of replication: It is the sequence of genome where the DNA replication starts.


2. Ampicillin resistance site: It codes for the Ampicillin resistant gene.


3. Tetracycline resistance site: It codes for the Tetracycline resistant gene.


4. Bam H1 restriction site: It recognizes short DNA strands and cleaves them at a specific site.


pBR322 structure:



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(b) Analyse the reason for different positions taken up by the DNA bands.


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