Which of the following steps are related to polymerase chain reaction…

The correct answer is Option (1) → (A), (B) and (D) only

Polymerase chain reaction (PCR) makes many copies of a chosen piece of DNA in a test tube. It uses two primers and a heat-stable DNA polymerase (Taq polymerase). Each cycle has three steps, repeated again and again.

(A) Extension — Correct. The polymerase extends each primer, building a new strand on the template.

(B) Annealing — Correct. On cooling, the primers bind to their complementary regions on the single strands.

(C) Propagation — Incorrect. Propagation means growing or spreading, for example of plants or cultures. It is not a step of PCR.

(D) Denaturation — Correct. High temperature separates the two strands of the DNA. This is the first step of each cycle.

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.”