 Alright pedigrees, as I said, are about the fact that we can't just go out and madly produce human babies and then see what they look like and then dump them out somewhere. That does not happen. So instead we can evaluate history and analyze relationships and see if we can learn from the babies that have been made in a family and see what we can figure out. Okay, so a couple things that you need to know about pedigree analysis. First of all, squares are anatomically male humans. Circles are female humans. Connections between them, horizontal connections are baby-making events. We used to say, those are marriages, but I don't think we need to say that. We just need to say that we made babies together and then look carefully at this. Things that are connected with horizontal lines are siblings. I don't know if that's clear, but these are siblings. So let's look at this example. I have pedigree A sitting here and it's super simple so that we can see. We have a male, we have a female, they had a baby-making event, and then they produced every one of these things is produced. Those are humans. Every one of those humans was produced by the baby-making events of the top two people. So some things that we could say. The top two people made two boys and two girls. One of the boys is affected. So a filled-in circle. Any filled-in shape equals an affected phenotype. Oops, we don't have to put an eye there. Okay, one boy is affected. No girls are affected. What can we, is there anything we can figure out about this condition? We don't even know anything about what it is. Well, how did the boy get affected if there's no, if the parents aren't affected? Right there, you should say, oh, this must be a recessive trait because we have one affected kid that like somehow that kid got its genetics from its parents. Okay, so we have the trait is recessive. What does that tell you about the parents? Well, I suppose it might tell us something maybe about, like I wonder if this could be a sex-linked trait. It's possible, but it definitely tells you that at least one of the parents is a carrier, right? So let's just say, let's see if it could be a recessive trait not linked to a chromosome. Let's just see. And I'll just make up a letter. I'm gonna do big a little a. And I'm gonna say like, let's see if this works that we could say big a little a for both parents. And then that would mean that the kid would have little a little a recessive, homozygous recessive, and that would show up. Is it possible that none of the other kids would get the trait? Totally. I mean, they could all of them have to get at least one dominant allele. And who knows, they could get two dominant alleles. That would work because they have a dominant allele to get from each parent. You could go through and make a square for this scenario and convince yourself that yes, it is possible. In fact, possible and like the numbers, the percentages match up. Keep in mind the percentages are probabilities. So it doesn't have to match up. That's not a slam dunk. But I would say that this is possible that it's an autosomal recessive trait possible. Should we see if it's possible for it to be a sex linked recessive trait? Let's see. Okay. I'm afraid that in order to make it sex linked, watch what I'm going to do. I'm going to take this and say yes, it is possible and we're just going to throw it up here even though it's like a mess. And then I'm going to erase everything that I said about this now and I'm going to try it if it's sex linked. Okay. If it's sex linked, let's just say X linked. Because if it's Y linked, then both boys would have it, right? So we know it's not Y linked. Here's X dad. Dad doesn't have it. So I'm going to use the same letters, big A. Mom has to, she doesn't have it, but she has to have the recessive allele, right? And she has to give that recessive allele to her son because the son got the X chromosome or the Y chromosome from dad. Are you cool? All boys get their Y chromosomes from their dads, all of them and everyone gets their X from their mom. Girls get an X from their dad. Dads only give X's to their girls. And I say that anatomically, not genderly. Okay. We know this person has to have a Y chromosome, but doesn't express the condition. So they have to be X, big A. And now we have two girls who do not express. So we have to say they have at least one dominant allele and who knows? Oh, maybe I should say they do have an X, but who knows what flavor of X they have. They could be carriers given this scenario where they could be homozygous dominant. Could it be sex-linked trait? I think it could be. I don't see any reason that this isn't a sex-linked trait. Pedigrees are puzzles. They're not easy. You don't just do a pedigree and voila, everything becomes clear. Sometimes it does and that's fun. We're going to do one more pedigree practice, but let's just see. We're going to do a similar thing as this and see what the possible inheritance pattern is from another one.