Final answer:
The technique used to determine the initial quantity of template DNA in PCR cycles is known as quantitative PCR or qPCR, which utilizes fluorescence to quantify the original target sequence.
Step-by-step explanation:
The technique that allows one to determine the amount of template DNA present when the PCR cycles began is quantitative PCR (qPCR). This method employs the use of fluorescence to monitor the increase in double-stranded DNA as the reaction occurs. By analyzing the kinetics data, the amount of the original target sequence in the sample before the PCR process commenced can be quantified. qPCR can also be used to detect not only the presence but also the relative amounts of specific transcripts in a sample, making it a powerful tool for studies on differential gene expression and gene regulation.