Quantitative PCR (qPCR), also known as real-time PCR, is the gold standard for gene quantification. 

qPCR is a highly sensitive and specific technique that allows for both detection and quantification of the PCR product in real-time, while it is being synthesized. 

The technique relies on the amplification of a target gene through the use of specific primers and fluorescent probes. It provides information beyond mere detection of DNA. It also indicates how much of a specific DNA or gene is present in the sample.The calculation of the relative expression of a target-gene by qPCR is based on the use of reference genes as endogenous control.

qPCR is widely used in research and clinical settings for a number of applications including gene expression analysis, genotyping, and pathogen detection.