Well, if we take this plant with the unknown genotype and we cross it with a plant whose genotype we actually know, then we can figure this problem out. And the only type of plant whose genotype we know for certain is a homozygous recessive. So a short plant, because the only time a plant will be short is if its genotype is actually lowercase T. Lowercase T. And this is what we call a test cross. 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.