Scientist, Brewer, Gardener, and Backyard Chicken Farmer
The PCR was designed to make millions of copies of only the Avr1 gene, which is found in Fusarium Race 1 and not Race 2 or 3. If the Fusarium in my plants is Race 1 we expect a bright band to show up on the agarose gel. It’s clear that the Fusarium growing in plants #1 and #2 is Fusarium Race 1 since a large spot of copied DNA is visible. Plant #3 is either Race 2 or Race 3 because no Avr1 was there to be copied and no band shows up on the agarose gel.