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Biology Unit 4
Topic 6: Infection, Immunity and Forensics
6. Describe how DNA can be amplified using the
polymerase chain reaction (PCR).
The polymerase chain reaction (PCR) allows small samples of DNA to be amplified so that they can
then be used in DNA profiling. The process relies on DNA primers, short sequences of DNA
complementary to the DNA adjacent to the STR. A cycle of temperature changes result in huge
numbers of the DNA fragments being produced.
1. Reactants placed in vials in PCR machine
2. STEP 1 90-95 °C for 30 seconds DNA strand separates
3. STEP 2 50-60°C for 20 seconds primers bind to DNA strands
4. STEP 3 75°C for at least a minute DNA polymerase builds up complementary strands of
5. STEP 1-3 repeated
Text Book: p.80-81