reverse transcription polymerase chain reaction, a variant of polymerase chain reaction (PCR), a technique commonly used to detect RNA expression.RT-PCR is not to be confused with real-time polymerase chain reaction (qPCR). RT-PCR is used to qualitatively detect gene expression through the creation of complementary DNA (cDNA) transcripts from RNA. A common application of PCR is the study of patterns of gene expression. Tissues (or even individual cells) can be analyzed at different stages to see which genes have become active, or which have been switched off. This application can also use quantitative PCR to quantitate the actual levels of expression. qPCR is used to quantitatively measure the amplification of DNA using fluorescent dyes. qPCR is also referred to as quantitative PCR, quantitative real-time PCR, and real-time quantitative PCR. Although RT-PCR and the traditional PCR both produce multiple copies of particular DNA isolates through amplification, the applications of the two techniques are fundamentally different. Traditional PCR is used to exponentially amplify target DNA sequences. RT-PCR is used to clone expressed genes by reverse transcribing the RNA of interest into its DNA complement (cDNA) through the use of reverse transcriptase. Subsequently, the newly synthesized cDNA is amplified using traditional PCR.