<prompt> The graph below depicts a polymerase chain reaction inDNA PCRPCRNested PCRReal time PCR  <response>: A quantitative polymerase chain reaction qPCR, also called real-time polymerase chain reaction, is a laboratory technique of molecular biology based on the polymerase chain reaction PCR, which is used to amplify and simultaneously quantify a targeted DNA molecule. For one or more specific sequences in a DNA sample, quantitative PCR enables both detection and quantification. The quantity can be either an absolute number of copies or a relative amount when normalized to DNA input or additional normalizing genes. The procedure follows the general principle of polymerase chain reaction; its key feature is that the amplified DNA is detected as the reaction progresses in real time. This is a new approach compared to standard PCR, where the product of the reaction is detected at its end. Two common methods for the detection of products in quantitative PCR are: 1 non-specific fluorescent dyes that intercalate with any double-stranded DNA, and 2 sequence-specific DNA probes consisting of oligonucleotides that are labelled with a fluorescent repoer which permits detection only after hybridization of the probe with its complementary sequence to quantify messenger RNA mRNA and non-coding RNA in cells or tissues. 