Assertion (A):
Restriction enzymes cut the strand of DNA a little away from the centre of the palindromic site, creating sticky ends.
Reason (R):
These sticky ends are necessary because they facilitate the action of the enzyme DNA ligase by forming hydrogen bonds with their complementary cut counterparts.

[Biotechnology-Principles-and-Processes] [class-xii ]

• (A) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion
• (B) Both Assertion and Reason are true, but Reason is not the correct explanation of Assertion
• (C) Assertion is true but Reason is false
• (D) Assertion is false but Reason is true
Correct Option: A  [ A ]

Remark: A is True: Restriction enzymes cut away from the center of the palindrome, leaving single-stranded portions called sticky ends.
R is True: The stickiness facilitates DNA ligase action as they bond with complementary ends. R explains why the structure created in A is useful.

Assertion (A):
The linking of the cut antibiotic resistance gene with the plasmid vector to form recombinant DNA became possible with the enzyme DNA ligase.
Reason (R):
If the vector DNA and the source DNA are cut by the same restriction enzyme, the recombinant molecule cannot be created.

[Biotechnology-Principles-and-Processes] [class-xii ]

• (A) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion
• (B) Both Assertion and Reason are true, but Reason is not the correct explanation of Assertion
• (C) Assertion is true but Reason is false
• (D) Assertion is false but Reason is true
Correct Option: C  [ C ]

Remark: A is True: DNA ligase acts on cut DNA molecules and joins their ends, creating recombinant DNA.
R is False: Normally, the vector and source DNA must be cut by the *same* restriction enzyme to generate the necessary matching sticky ends for ligation.

Assertion (A):
Exonucleases remove nucleotides from the ends of the DNA, whereas endonucleases make cuts at specific positions within the DNA.
Reason (R):
Restriction enzymes belong to a larger class of enzymes called nucleases.

[Biotechnology-Principles-and-Processes] [class-xii ]

• (A) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion
• (B) Both Assertion and Reason are true, but Reason is not the correct explanation of Assertion
• (C) Assertion is true but Reason is false
• (D) Assertion is false but Reason is true
Correct Option: B  [ B ]

Remark: A is True: This correctly defines the functional difference between exonucleases and endonucleases.
R is True: Restriction enzymes are a type of nuclease. R provides the class name, but does not explain the functional differences detailed in A.

Assertion (A):
The palindromic sequence in DNA reads the same on the two strands when the orientation of reading (e.g., 5' to 3') is kept the same.
Reason (R):
The first restriction endonuclease, Hind II, always cut DNA molecules by recognising a specific sequence of six base pairs.

[Biotechnology-Principles-and-Processes] [class-xii ]

• (A) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion
• (B) Both Assertion and Reason are true, but Reason is not the correct explanation of Assertion
• (C) Assertion is true but Reason is false
• (D) Assertion is false but Reason is true
Correct Option: B  [ B ]

Remark: A is True: This is the definition of a palindromic sequence in DNA.
R is True: Hind II recognizes a specific sequence of six base pairs. Both statements are facts, but R does not explain or justify the definition of the DNA palindrome in A.

Assertion (A):
When an alien piece of DNA is transferred into an alien organism, it needs to be linked with the origin of replication (`ori`).
Reason (R):
The origin of replication sequence is responsible for initiating replication and also controls the copy number of the linked DNA.

[Biotechnology-Principles-and-Processes] [class-xii ]

• (A) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion
• (B) Both Assertion and Reason are true, but Reason is not the correct explanation of Assertion
• (C) Assertion is true but Reason is false
• (D) Assertion is false but Reason is true
Correct Option: A  [ A ]

Remark: A is True: For an alien DNA piece to multiply in the host, it must be linked to the `ori`.
R is True: The `ori` sequence is specifically responsible for initiating replication and controlling the copy number. R explains why the linkage described in A is essential for multiplication.

Assertion (A):
Cloning vectors must have very few, preferably single, recognition sites for commonly used restriction enzymes.
Reason (R):
Presence of more than one recognition site within the vector will generate several fragments, which will complicate the gene cloning process.

[Biotechnology-Principles-and-Processes] [class-xii ]

• (A) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion
• (B) Both Assertion and Reason are true, but Reason is not the correct explanation of Assertion
• (C) Assertion is true but Reason is false
• (D) Assertion is false but Reason is true
Correct Option: A  [ A ]

Remark: A is True: Vectors are engineered to have very few restriction sites.
R is True: The complication (R) resulting from multiple cuts is the specific reason for the necessity stated in A.

Assertion (A):
Genes conferring resistance to antibiotics are considered useful selectable markers in cloning experiments.
Reason (R):
Selectable markers help in identifying and eliminating non-transformants by selectively permitting the growth of only the transformants.

[Biotechnology-Principles-and-Processes] [class-xii ]

• (A) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion
• (B) Both Assertion and Reason are true, but Reason is not the correct explanation of Assertion
• (C) Assertion is true but Reason is false
• (D) Assertion is false but Reason is true
Correct Option: B  [ B ]

Remark: A is True: Antibiotic resistance genes (like ampicillin or tetracycline) are commonly used selectable markers.
R is True: R defines the general function of a selectable marker. Although related, R is the general goal, not the specific mechanism or justification for *using* antibiotic resistance genes (which rely on the fact that normal E. coli lacks resistance).

Assertion (A):
If a foreign DNA is ligated at the $BamH$ I site in the vector pBR322, the transformant cells will lose resistance to ampicillin.
Reason (R):
The $BamH$ I restriction site is present within the coding sequence of the tetracycline resistance gene ($tet^R$) of pBR322.

[Biotechnology-Principles-and-Processes] [class-xii ]

• (A) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion
• (B) Both Assertion and Reason are true, but Reason is not the correct explanation of Assertion
• (C) Assertion is true but Reason is false
• (D) Assertion is false but Reason is true
Correct Option: D  [ D ]

Remark: A is False: Ligation at the $BamH$ I site inactivates the *tetracycline* resistance gene ($tet^R$), not the ampicillin resistance gene ($amp^R$).
R is True: The $BamH$ I site is located within the $tet^R$ gene of pBR322.

Assertion (A):
Selection of recombinants using insertional inactivation of the $eta$-galactosidase gene is often preferred over selection using two antibiotic resistance genes.
Reason (R):
Non-recombinant colonies carrying the intact $eta$-galactosidase gene appear blue in the presence of a chromogenic substrate.

[Biotechnology-Principles-and-Processes] [class-xii ]

• (A) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion
• (B) Both Assertion and Reason are true, but Reason is not the correct explanation of Assertion
• (C) Assertion is true but Reason is false
• (D) Assertion is false but Reason is true
Correct Option: B  [ B ]

Remark: A is True: Using color production is an alternative developed because selection involving two antibiotic plates is cumbersome.
R is True: Non-recombinants, which have the active $eta$-galactosidase gene, produce blue colonies in the presence of a chromogenic substrate. R describes the visible outcome but does not explain *why* the method is preferred (which is because it avoids simultaneous plating).

Assertion (A):
Bacterial cells are made 'competent' to take up DNA by treating them with divalent cations such as calcium.
Reason (R):
DNA is a hydrophilic molecule, so it cannot pass easily through the hydrophobic cell membrane without chemical manipulation.

[Biotechnology-Principles-and-Processes] [class-xii ]

• (A) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion
• (B) Both Assertion and Reason are true, but Reason is not the correct explanation of Assertion
• (C) Assertion is true but Reason is false
• (D) Assertion is false but Reason is true
Correct Option: A  [ A ]

Remark: A is True: Competence is achieved by treatment with divalent cations like calcium.
R is True: DNA is hydrophilic, which is the chemical reason why it needs the competency treatment (A) to cross the hydrophobic membrane. R explains A.