Absolute and relative gene expression in Listeria monocytogenes using real-time PCR

Reverse transcription combined with the polymerase chain reaction (RT-PCR) is a viable method widely used to quantify gene expression. There are two ways to quantify gene expression by real-time PCR: relative quantification and absolute quantification. Relative quantification relates the PCR signal of the target gene to a control gene, normally a housekeeping gene. Absolute quantification determines the input copy number, usually by relating the PCR signal to a standard curve. Here we describe both methods from RNA extraction to its quantification by real-time PCR.