 All right, my friendlies, we're going to do a punnett square and I'm going to tell you the steps that we will always use and I'm going to use the exact same example that we've done. First of all, punnett squares are little math problems and showing your work and being, what, disciplined about keeping track of what you're doing is important because that will show you where, if there are any mistakes that are made. So be disciplined about following this exact process each time you do a punnett square. We have a white P mama and a purple P papa and we're going to make some P babies. The first thing you have to do is you have to identify the parent phenotypes. Often the parent phenotypes are given and in this case, it's totally true. We have a white P mama. This is a parental phenotype and a purple P papa. We don't know if the purple P is the papa or the white P is the papa. It doesn't matter. I'm just making it up because purple P papa sounds way cooler than white P papa. White P mama sounds way cooler than white P papa. Nobody understands. Once you have your parent phenotypes, you need to know their genotypes and this, at some point, something is probably going to have to be figured out. In this case, I told you way back in the beginning that these were true breeding and that tells you right now the genotype. You need to know some information about these P plants and you'll probably get that in the problem. We already know that the white trait is recessive. It's coded for by the recessive allele. And so we know that the genotype of the white P mama is homozygous recessive, little P. We know the genotype of the true breeding purple P papa is homozygous dominant. We now have the genotype and the genotype. The next step is to go through meiosis. So I'm going to show it in yellow because meiosis is so cool. It's my favorite color. And what's the end result of meiosis clowns? I call you clowns in the most loving way possible. The end result are gametes, doggies, gametes. So the next question are, what are all the possible gametes from each parent? Now, imagine, if you will, that this is all we're doing here is we're showing that, oh, this is going to hurt my head, but please bear with me. All we're doing is we're showing that on both the white P mamas chromosomes, we have the little P allele. And on both the purple P's papa's chromosomes, he has the big P allele. So if you go through meiosis, you don't even have to go through all your stages. Just go through anaphase two of meiosis two, and you can see that we're just going to end up with a little P allele and a little P allele in our gametes. So, dude, your possible gametes are going to look like this. I like to circle my gametes. I know that there are two from this visual, there are two, but those are exactly the same, so I don't have to write it two times. I mean, how many possible, how many gametes does a white P mama make? Probably like billions. I'm not going to write out every single one of them. I'm only going to write out all the different ones, so I'm only going to write this once. Here's my gamete. Could my gamete be, this is a question for you, could my gamete be like that? Could that be the result of meiosis? If you think it is, go back and review meiosis and look at it over and over and over again until you're comfortable that no, no, no, no, no. A gamete cannot be diploid. A gamete that's diploid is going to end up with a baby that's like quadruploid and that's going to be all bad for the baby. That baby ain't going to live. So what are the possible gametes for my purple P parent? My purple P papa, he can only donate big P alleles, which means that after meiosis, he's going to end up with only big P sperm. Are you ready for the Punnett square? This is how a Punnett square works. I'm going to make it really tiny because I don't want to go to a new page. All you do, this is, my next step is Punnett square. Punnett square. Step one, identify the phenotype. Step two, the genotype. Step three, possible gametes. Step four, Punnett square. In a Punnett square, you put one parent's gametes on one side. All the possible gametes. In this case, there's one possible gamete. And the other parent's possible gametes on the other side, all the possible gametes. In this case, there's only one. And then you just do a random like, what would happen if this sperm combined with this egg? We would end up with a baby that looked like this. Now you know. Here's my baby. That's a zygote. And you can look at that and say its genotype is heterozygous. What's that pee baby going to look like? It's going to be purple. It's going to be purple flowered. And what percentage of all of the babies will have purple flowers? 100% purple. Do you agree with that? You just made a Punnett square. Shall we try something a little more complicated? We'll do a monohybrid cross. Because now we're going to get to see like that. You might look at that and be like, dude, I did not have to make a Punnett square in order to figure that out. That's cool. That's very cool. But the Punnett square process is important. Let's do it with something called a monohybrid cross. Mono-e-mono-hybrid cross.