My work colleague ran an experiment and his water control, all four of them came back positive. Now the intriguing part is that the bands had an identical intensity to his positive wells and the bands were also the same size.
He has decided to lay the blame on contaminated pipettes rather than making a mistake. The pipettes are general purpose and are used for all sorts of reagents and DNAs, filtered tips are also used.
So what is the likely hood of not one but both primers binding onto foreign DNA and also amplifying a fragment of DNA that is an identical size to his target DNA? Not only that but if the pipette was contaminated, the DNA happened to be identical to the DNA being used in his experiment.
With all these coincidences what, out of contamination and user error, which do you think is more likely?