Assertion (A):
Each restriction endonuclease functions by binding to the DNA and cutting each of the two strands of the double helix at specific points in their sugar-phosphate backbones.
Reason (R):
Each restriction endonuclease recognizes a specific palindromic nucleotide sequence in the DNA by inspecting the length of the DNA sequence.

[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 bind and cut the sugar-phosphate backbone.
R is True: The cutting (A) is specific because the enzyme first inspects the DNA and finds its specific palindromic recognition sequence. R explains the prerequisite for A.

Assertion (A):
Restriction enzymes cut the DNA strands a little away from the center of the palindrome sites, leaving single-stranded portions called sticky ends.
Reason (R):
These sticky ends form strong covalent bonds with their complementary cut counterparts, which facilitates the action of DNA ligase.

[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: Restriction enzymes cut away from the center, creating sticky ends.
R is False: Sticky ends form *hydrogen bonds* with complementary counterparts. DNA ligase then seals the backbone.

Assertion (A):
Recombinant molecules of DNA are composed of DNA from different sources/genomes.
Reason (R):
Normally, the vector and the source DNA must be cut by the same restriction enzyme to ensure that the resultant fragments have the same kind of sticky ends.

[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: Recombinant DNA combines DNA from different sources.
R is True: Using the same enzyme is required because it generates matching sticky ends needed for ligation. R explains the necessary step to create A.

Assertion (A):
DNA fragments are separated in gel electrophoresis according to their size.
Reason (R):
The agarose matrix provides a sieving effect, causing smaller DNA fragments to move farther through the gel towards the anode.

[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: Fragments separate based on size.
R is True: The sieving effect of agarose causes smaller fragments to move farther. R explains the physical mechanism that achieves the separation described in A.

Assertion (A):
Pure DNA fragments are visible in the gel only after staining with ethidium bromide and exposure to UV radiation.
Reason (R):
Pure DNA fragments are not visible in visible light and without staining.

[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: Visualization requires staining and UV exposure.
R is True: This explains the necessity for the procedure described in A.

Assertion (A):
The process of cutting out the separated bands of DNA from the agarose gel and extracting them from the gel piece is known as elution.
Reason (R):
The DNA fragments purified through elution are then used in constructing recombinant DNA by joining them with cloning vectors.

[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: Elution is the process of extracting DNA from the gel pieces.
R is True: The purified fragments are used for ligation into vectors. R explains the importance of the DNA recovered by the process described in A.

Assertion (A):
The origin of replication ($ori$) sequence in a vector is responsible for controlling the copy number of the linked DNA.
Reason (R):
If a scientist wants to recover many copies of the target DNA, it should be cloned in a vector whose origin supports a high copy number.

[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: The $ori$ controls the copy number.
R is True: The desired copy number (R) dictates which vector (A) must be selected. R justifies the cloning strategy based on the function stated in A.

Assertion (A):
Vectors need to 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 complicate the gene cloning process by generating several fragments.

[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 for single sites.
R is True: The generation of multiple fragments (R) is the reason why A is essential. R explains A.

Assertion (A):
If a foreign DNA is ligated at the $Pst$ I site in the vector pBR322, the recombinant plasmid loses resistance to ampicillin.
Reason (R):
The $Pst$ I restriction site is present within the coding sequence of the $tet^R$ gene 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: C  [ C ]

Remark: A is True: $Pst$ I is located in the $amp^R$ gene, leading to ampicillin resistance loss [31, Figure 9.4].
R is False: $Pst$ I is in the $amp^R$ gene. The $BamH$ I and $Sal$ I sites are in the $tet^R$ gene [31, Figure 9.4].

Assertion (A):
Selection of recombinants using insertional inactivation of the $eta$-galactosidase gene is often preferred because it avoids the cumbersome procedure of simultaneous plating on two plates having different antibiotics.
Reason (R):
The general principle of insertional inactivation is that the foreign DNA is inserted within the coding sequence of a gene, making it non-functional.

[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: Color-based selection avoids the cumbersome two-plate antibiotic method.
R is True: R defines the general mechanism of insertional inactivation. R explains how the color system works, but not why it is *preferred* over the antibiotic method (A).