What is a typical initial step when using a thermal cycler?

• A. Set the thermal cycler to the appropriate program
• B. Place PCR tubes into the block after selecting no program
• C. Run without setting a program
• D. Set the program after starting the run

Answer: (A)

The key idea is that a PCR run must follow a defined thermal cycling program that tells the instrument which temperatures and times to apply for each step (denaturation, annealing, extension). Because the machine needs these instructions to perform the cycles correctly, the initial step is to set the thermal cycler to the appropriate program. Once the program is loaded, you typically place the PCR tubes in the block and then start the run. Trying to run without a program or starting before the program is set would leave the instrument without instructions, so no amplification would occur.