Assertion (A): In insertional inactivation using a chromogenic substrate, non-recombinant colonies appear blue. Reason (R): The presence of an insert results in the inactivation of the $eta$-galactosidase gene, causing the colonies to remain colorless and thus identifying them as recombinants.
A is True: Non-recombinants have the intact gene and produce the blue color. R is True: The lack of color production due to insertional inactivation identifies the recombinants. R describes the mechanism that allows the differentiation based on the color status detailed in A.
Question 512 of 535
📘 CLASS XII
Assertion (A): We learned the lesson of transferring genes into plants and animals from studying bacteria and viruses. Reason (R): Pathogens like Agrobacterium tumifaciens (in plants) and retroviruses (in animals) naturally possess the ability to deliver genes to transform eukaryotic cells.
A is True: Knowledge of gene transfer originated from observing pathogens. R is True: R lists the pathogens that provided this key knowledge. R explains the source of the lesson mentioned in A.
Question 513 of 535
📘 CLASS XII
Assertion (A): The tumor inducing ($Ti$) plasmid of Agrobacterium tumifaciens is used in its pathogenic form as a cloning vector for gene delivery into dicot plants. Reason (R): The Ti plasmid has been modified into a cloning vector that is no longer pathogenic but is still able to deliver genes of interest into a variety of plants.
A is False: The Ti plasmid must be modified to be non-pathogenic for use as a vector. R is True: The modified Ti plasmid is non-pathogenic yet effective for gene delivery.
Question 514 of 535
📘 CLASS XII
Assertion (A): Bacterial cells are treated with a divalent cation like calcium to make them 'competent' to take up DNA. Reason (R): The calcium treatment increases the efficiency with which the DNA enters the bacterium through pores in its cell wall.
A is True: Divalent cations like calcium are used to induce competence. R is True: The mechanism by which this works is by increasing the efficiency of DNA entry through cell wall pores. R explains A.
Question 515 of 535
📘 CLASS XII
Assertion (A): Micro-injection is a method of introducing recombinant DNA by bombarding cells with high velocity micro-particles of gold or tungsten coated with DNA. Reason (R): Micro-injection is suitable for plant cells, while biolistics (gene gun) is suitable for animal cells.
A is False: A describes biolistics or gene gun. Micro-injection involves direct injection into the nucleus of an animal cell. R is False: Micro-injection is for animal cells; biolistics is suitable for plant cells.
Question 516 of 535
📘 CLASS XII
Assertion (A): In order to cut DNA with restriction enzymes, the DNA needs to be in pure form, free from other macromolecules. Reason (R): DNA is contained within membranes, and we must break the cell open to release DNA along with other macromolecules such as RNA, proteins, and polysaccharides.
A is True: DNA must be purified before restriction enzyme digestion. R is True: Cell lysis is required to release DNA along with contaminants. Both are necessary steps, but R explains the state of DNA in the cell, not why it must be pure before cutting (A).
Question 517 of 535
📘 CLASS XII
Assertion (A): To isolate DNA, bacterial cells are treated with lysozyme, plant cells with cellulase, and fungal cells with chitinase. Reason (R): These specific enzymes are used to break down the respective cell walls to achieve the release of DNA.
A is True: These enzymes are correctly matched to their respective cell types. R is True: The goal of using these enzymes is to break the cell boundaries to release DNA. R explains A.
Question 518 of 535
📘 CLASS XII
Assertion (A): RNA is removed from the DNA extract by treatment with ribonuclease, and proteins are removed by protease. Reason (R): Genes are located on long molecules of DNA intertwined with proteins such as histones.
A is True: Ribonuclease and protease are used for removing RNA and protein contaminants. R is True: DNA is associated with proteins like histones. R describes the structure, but not why the contaminants must be digested (A).
Question 519 of 535
📘 CLASS XII
Assertion (A): Agarose gel electrophoresis is used to check the progression of a restriction enzyme digestion. Reason (R): After digestion, the DNA is a negatively charged molecule, and it must move towards the positive electrode (anode) under an electric field.
A is True: Gel electrophoresis is used to verify digestion. R is True: DNA is negative and moves toward the anode. R describes the physical property necessary for the separation seen in A, but not why A is used to check the digestion.
Question 520 of 535
📘 CLASS XII
Assertion (A): In Polymerase Chain Reaction (PCR), the segment of DNA can be amplified to approximately a billion times after many repeated cycles. Reason (R): Such repeated amplification is achieved by using a thermostable DNA polymerase, which remains active during the high temperature denaturation steps.
A is True: DNA can be amplified to a billion copies in PCR. R is True: The thermostable polymerase (like *Taq*) allows the cycles (including high heat steps) to be repeated many times efficiently, which is necessary to achieve the huge amplification mentioned in A. R explains how A is achieved.
