How does real-time PCR (qPCR) enable quantification of nucleic acids?

Real-time PCR monitors DNA amplification during each cycle using fluorescent reporters. SYBR Green intercalates into double-stranded DNA, fluorescing when bound. TaqMan probes use oligonucleotides with fluorophore and quencher that separate upon polymerase cleavage. The cycle threshold (Ct) - when fluorescence exceeds background - is inversely proportional to initial template amount. Absolute quantification uses standard curves, while relative quantification compares target to reference genes (delta-delta Ct method). qPCR is essential for gene expression analysis, pathogen detection, and validating other techniques like RNA-seq.