Read the passage carefully and answer the given questions.
Recombinant DNA Technology
Asexual reproduction preserves the genetic information, while sexual reproduction permits variation. Traditional hybridization procedures used in plants and animals breeding very often lead to inclusion and multiplication of undesirable genes along with the desired genes. The techniques of genetic engineering, which include creation of recombinant DNA, use of gene cloning and gene transfer, overcome this limitation and allow us to isolate and introduce only one or a set of desirable genes without introducing undesirable genes into the target organism.
Which one of the following techniques is used to amplify a specific DNA sequence?
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → Polymerase Chain Reaction (PCR)
Option (1) Polymerase Chain Reaction (PCR) — Correct. Each cycle of PCR has three steps: denaturation, annealing of the primers and extension. The DNA doubles in every cycle, so a chosen piece is amplified to a very large number of copies in a short time.
Option (2) Gel Electrophoresis — Incorrect. Gel electrophoresis separates DNA fragments by size in an electric field. It sorts the fragments that are already present; it does not make new copies.
Option (3) Northern Blotting — Incorrect. Northern blotting detects a particular RNA. The RNA is separated in a gel, moved onto a membrane and found with a labelled probe. It works on RNA and does not copy DNA.
Option (4) DNA Sequencing — Incorrect. Sequencing reads the order of the bases in a DNA molecule. It gives information about the DNA but does not increase its amount.
Note: This passage is taken from NCERT as it is. Most CUET (UG) questions come straight from NCERT, so study the book line by line, including figures and their titles.
NCERT Extract:
Amplification of Gene of Interest Using PCR – “… PCR stands for Polymerase Chain Reaction. In this reaction, multiple copies of the gene (or DNA) of interest is synthesised in vitro using two sets of primers (small chemically synthesised oligonucleotides that are complementary to the regions of DNA) and the enzyme DNA polymerase. The enzyme extends the primers using the nucleotides provided in the reaction and the genomic DNA as template. If the process of replication of DNA is repeated many times, the segment of DNA can be amplified to approximately billion times, i.e., 1 billion copies are made.”