CBSE Class 12-science Answered

(i) Downstream processing refers to the recovery and purification of products- Incorrect

(ii) The disarmed pathogen vectors are used because the vectors have been genetically modified so that the virulent and the pathogen properties are not there. It is a more efficient process of transferring the DNA in to the host without any risk of infection or mistakes- Correct

(iii) Taq polymerase is heat tolerant with the optimum temperature activity being 75-80 degree Celcius. It was specifically chosen to execute Polymerase Chain Reactions (PCR), because it was able to survive the high temperatures required to denature the DNA duplex- Correct

(iv) In the laboratory setting, Pfu is used to amplify DNA in the polymerase chain reaction (PCR), where the enzyme serves the central function of copying a new strand of DNA during each extension step- Correct

(v) Gel electrophoresis is a technique used to separate DNA fragments based on their size and charge- Incorrect.

From the above statements, there are two incorrect statements, statement (i) and (v)

So, option (4) is correct.