I am doing RT-PCR. For internal control, I am amplifying beta actin. However, all the samples are showing different intensities of bands. In order to get same amount of beta-actin amplification, at which step, should I quantitate the template for all different samples? RNA step? or cDNA step? Do I have to start with same amount of RNAs before cDNA synthesis? Or is it ok to quantitate cDNA after cDNA synthesis for adding same amount of PCR template?