A test cross is this experiment that basically allows us determine which one of these genotypes it actually is. So by crossing our unknown genotype with a known genotype, we can determine what that initial genotype is. So let's actually see how that works. Now, let's begin by assuming that the genotype of my unknown plant is this. Okay, so we begin by assuming the genotype is this. And now we want to basically carry out the pundits square experiment.