Tools of Recombinant DNA Technology - Free MCQ Practice Test with solutions,

• The separated bands of DNA are cut out from the agarose gel and extracted from the gel piece.
• This step is known as elution.

Line in NCERT: "The separated bands of DNA are cut out from the agarose gel and extracted from the gel piece. This step is known as elution."

The origin of replication (ori) is crucial for initiating the replication of the DNA within the host cells, ensuring that the DNA is copied during cell division.

Ncert Topic: Cloning Vectors

Ncert line: Origin of replication (ori) : This is a sequence from where replication starts and any piece of DNA when linked to this sequence can be made to replicate within the host cells. This sequence is also responsible for controlling the copy number of the linked DNA

The drug resistance gene against penicillin is not typically used as a selectable marker in E. coli, as it does not provide a reliable means of selection compared to other antibiotic resistance genes.

Ncert Topic: Cloning Vectors ( Selectable Marker)

Ncert Line: Normally, the genes encoding resistance to antibiotics such as ampicillin, chloramphenicol, tetracycline or kanamycin, etc., are considered useful selectable markers for E. coli.

Option C is correct.

• Statement i is correct: Hind II was the first restriction endonuclease characterised and it recognises and cuts a specific six-base-pair DNA sequence.

• Statement ii is incorrect: the standard naming convention uses the first letter of the genus and the first two letters of the species (for example, Eco from Escherichia coli), not the first two letters of the genus and one letter of the species as stated.

• Statement iii is incorrect: restriction enzymes are a class of endonucleases that cut within DNA at specific recognition sites; exonucleases remove nucleotides from the ends of DNA and are not restriction enzymes.

• Statement iv is correct in the standard text: most restriction endonucleases recognise specific palindromic nucleotide sequences and cut at those sites.

Therefore, only statements i and iv are correct, which corresponds to Option C.

• Assertion (A) Analysis: The assertion is true because alternative selectable markers indeed facilitate a more efficient identification process for recombinant colonies, reducing the complexity associated with traditional antibiotic selection methods.
• Reason (R) Analysis: The reason is also true, as it accurately describes how these markers function by enabling visual differentiation through color change.
• Explanation: The reason directly explains the assertion, as the simplification of the identification process is a direct result of the color change method provided by alternative selectable markers.
• Ncert line: Selection of recombinants due to inactivation of antibiotics is a cumbersome procedure because it requires simultaneous plating on two plates having different antibiotics. Therefore, alternative selectable markers have been developed which differentiate recombinants from non-recombinants on the basis of their ability to produce colour in the presence of a chromogenic substrate.