What initial input is used in Reverse Transcriptase PCR (RT-PCR)?

In Reverse Transcriptase PCR (RT-PCR), the initial input used is mRNA. This method is specifically designed to transcribe RNA into complementary DNA (cDNA) using the enzyme reverse transcriptase. The process begins with the isolation of mRNA from a sample, which represents the expressed genes of the organism at a certain time or under specific conditions.

By using mRNA as the starting material, RT-PCR allows researchers to study gene expression levels by converting the mRNA into cDNA, which can then be amplified and analyzed. This is particularly useful for quantifying the abundance of specific mRNAs in a sample, providing insights into cellular processes and responses.

The other options, such as DNA, cDNA, and amplified DNA, do not serve as initial inputs in this specific context. DNA would typically be the starting material for standard PCR, while cDNA is produced as a result of the RT-PCR process. Amplified DNA refers to the products of the PCR amplification step, which comes after the reverse transcription of mRNA into cDNA.