Assertion (A): Downstream processing is a crucial step that follows the biosynthetic stage in biotechnology. Reason (R): Downstream processing includes separation, purification, formulation with preservatives, clinical trials, and strict quality control testing of the product.
A is True: Downstream processing occurs after the product is synthesized. R is True: R lists the various components of downstream processing and quality control. While R details the contents of A, it does not explain *why* A is necessary, making it an expansion of A rather than a causal explanation.
Question 462 of 535
📘 CLASS XII
Assertion (A): To isolate pure DNA for cutting by restriction enzymes, animal cells must be treated with enzymes like lysozyme and chitinase. Reason (R): Enzymes are required because the DNA is contained within cell membranes and needs to be released from other macromolecules like RNA and proteins.
A is False: Lysozyme is used for bacterial cells and chitinase for fungal cells. Animal tissues are simply broken open; specific enzymes for animal cell walls/membranes are not listed here as being required in the same way. R is True: The fundamental reason for using any lysis technique is to break the cells open and release DNA from surrounding macromolecules.
Question 463 of 535
📘 CLASS XII
Assertion (A): Restriction enzymes cut DNA strands in a particular fashion, which leaves single-stranded ‘sticky ends’ on the strands. Reason (R): These clipped ends make pasting together pieces of DNA from different sources a precise exercise.
A is True: Restriction enzymes cut the DNA specifically, creating sticky ends. R is True: The utility of sticky ends is that they facilitate the precise joining (pasting) of DNA pieces. R explains A.
Question 464 of 535
📘 CLASS XII
Assertion (A): Plasmid DNA acts as a vector to transfer an alien piece of DNA into the host organism. Reason (R): Plasmids are naturally occurring autonomously replicating circular extra-chromosomal DNA found in bacterial cells.
A is True: Plasmids are used as vectors to ferry DNA. R is True: Plasmids are autonomously replicating circular extra-chromosomal DNA. R defines the vector, but does not explain *why* it acts as a vector (which is its ability to link and replicate alien DNA).
Question 465 of 535
📘 CLASS XII
Assertion (A): The first step in genetically modifying an organism is the identification of DNA with desirable genes. Reason (R): The major utility of the biological world, historically, has been only as a source of food.
A is True: Identification of DNA with desirable genes is the first basic step in genetic modification. R is False: While historical utility included food, the overall approach also developed technologies for human comfort and welfare.
Question 466 of 535
📘 CLASS XII
Assertion (A): Genetic engineering techniques are necessary to overcome the limitations of traditional hybridisation procedures. Reason (R): Traditional hybridisation often leads to the inclusion and multiplication of undesirable genes along with the desired genes, which genetic engineering prevents.
A is True: Genetic engineering overcomes the limitations of traditional breeding. R is True: R details the specific limitation of traditional breeding (undesirable gene inclusion), which directly explains why the techniques in A were needed.
Question 467 of 535
📘 CLASS XII
Assertion (A): The Roman number following the name of a restriction enzyme, such as $EcoRI$, indicates the order in which the enzyme was isolated from that strain of bacteria. Reason (R): The letter 'R' in the name $EcoRI$ is derived from the genus of the prokaryotic cell from which it was isolated.
A is True: Roman numerals indicate the order of isolation from the strain. R is False: The letter 'R' is derived from the name of the *strain* (RY 13), while the genus is represented by the first letter (E).
Question 468 of 535
📘 CLASS XII
Assertion (A): Genes encoding resistance to antibiotics such as ampicillin or tetracycline are useful selectable markers for E. coli because normal E. coli cells naturally carry resistance against these antibiotics. Reason (R): A selectable marker helps in identifying and eliminating non-transformants while permitting the selective growth of the transformants.
A is False: Normal E. coli cells do *not* carry resistance against these antibiotics. R is True: This is the defined function of a selectable marker.
Question 469 of 535
📘 CLASS XII
Assertion (A): Cloning vectors must have very few, preferably single, recognition sites for commonly used restriction enzymes. Reason (R): The presence of multiple recognition sites within the vector will generate several fragments, which will complicate the gene cloning procedure.
A is True: Vectors need single recognition sites. R is True: Multiple sites complicate cloning by fragmenting the vector. R explains why A is necessary.
Question 470 of 535
📘 CLASS XII
Assertion (A): In insertional inactivation, colonies of non-recombinants carrying the intact $eta$-galactosidase gene appear white in the presence of a chromogenic substrate. Reason (R): The intact $eta$-galactosidase gene results in enzyme synthesis which converts the chromogenic substrate into a blue product.
A is False: Non-recombinant colonies, having the active $eta$-galactosidase, appear *blue*. Recombinants do not produce color. R is True: Intact gene produces the enzyme, yielding the blue product.
