 A test cross is a special cross done with a homozygous recessive individual times a dominant unknown. Mmm, the dominant unknown. Okay, a dominant unknown. That just means that they're showing, they're expressing the dominant phenotype, but you don't know the genotype. So the dominant phenotype is expressed, but the genotype is unknown. In this visual here, they use the letter Y. This is pod color, I think. And again, this is another one where I'm pretty sure that they flipped the colors that we have used with this visual. Sorry, but a dominant phenotype person, or P, could have a dominant homozygous dominant genotype or a heterozygous genotype. And if the critter is expressing the dominant phenotype, you may not know what their genotype is, but you do know that it could be either one. If you run a test cross, oops, not T's, if you cross the unknown individual with a known homozygous recessive individual for the same trait, and then look at the babies, you can figure out which babies, which, if the person was heterozygous or homozygous. And I'm saying persons and peas, it's the same difference. Now look, here we have a heterozygote, here we have a homozygote. Both of them are crossed with a homozygous recessive. All we did is a punnett square. We threw some gametes in there. I do want to say something about this situation here. Sure, go for it. Sometimes it's nice to have four boxes, but you don't need them. Though that second box is extra work, because you only have one possible gamete from the homozygous recessive parent. That's everything. Do you agree that that second column is just a repeat of the first column? I like to save time, and I just figure out what my possible gametes are going to be. And then I save time and only put those possible gametes in. I don't put both possible gametes, even though I know that we're going to have two and everybody gets two. But it's just a repeat, and it doesn't change the percentages. But notice, if the person I crossed with was heterozygous, we're going to have some heterozygous recessive offspring. If the original cross was homozygous dominant, there are no heterozygous recessive offspring. So from that test cross, you can determine the genotype of a dominant critter. That comes in handy. Okay, you are punnett squared. Don't be punnett squared, or be squared punnettly. Don't, what? I'm going to stop now. Okay, goodbye.