Relative RT-PCR: Relative quantifications of RT-PCR involves the co-amplification of an internal control simultaneously with the gene of interest. The internal control is used to normalize the samples. Once normalized, a direct comparison of relative transcript abundances across multiple samples of mRNA can be made. One precaution to note is that the internal control must be chosen so that it is not affected by the experimental treatment. The expression level should be constant across all samples and with the mRNA of interest for the results to be accurate and meaningful. Because the quantification of the results are analyzed by comparing the linear range of the target and control amplification, it is crucial to take into consideration the starting target molecules concentration and their amplification rate prior to starting the analysis. The results of the analysis are expressed as the ratios of gene signal to internal control signal, which the values can then be used for the comparison between the samples in the estimation of relative target RNA expression.[24][27][28