Question

My class is doing a PCR reaction where we are to extract DNA from a sample (one control, and the other one a test sample) to determine whether sequences common within genetically modified organisms are contained within them.

There is one question that asks:
What is the purpose of the GMO (genetically-modified organism)-positive control DNA?

Answer 1

whenever conducting an experiment , even as simple as a PCR reaction, one has to understand the virtues of a positive and negative controls:
positive control - in order to interpret a negative result in the PCR to, lets say no GMO sequence, rather than a technical blunder - that might lead to a false negative - no PCR band for GMO even though it was clearly so (lets say MONSANTO's species of maze).
negative control - to verify that there is no contamination (for example that the primers do not contain by mistake GMO sequence) - thus enabling us to call a postive band for GMO as such and not as a false positive.