The polymerase chain reaction:

• A. Doubles the template sequence of DNA with each cycle.
• B. Makes a single copy of the template sequence of DNA with each cycle.
• C. Is used to determine the sequence of a region of DNA.
• D. All are correct.

Answer: (A)

Verified step by step guidance

1. Understand the purpose of the polymerase chain reaction (PCR): PCR is a technique used to amplify a specific segment of DNA, making millions of copies of a particular DNA sequence.
2. Identify the key steps in a PCR cycle: Denaturation (heating the DNA to separate strands), Annealing (cooling to allow primers to bind to the target sequence), and Extension (DNA polymerase extends the primers to form a new DNA strand).
3. Recognize that each cycle of PCR doubles the amount of DNA: During the extension step, the DNA polymerase synthesizes a new strand complementary to the template strand, effectively doubling the DNA with each cycle.
4. Consider the options given: The first option states that PCR doubles the template sequence with each cycle, which aligns with the fundamental principle of PCR.
5. Evaluate the other options: Making a single copy per cycle is incorrect as PCR is designed to exponentially amplify DNA. Determining the sequence of DNA is not the primary function of PCR, although it can be used in conjunction with sequencing techniques.