 All right, let's analyze this pedigree puzzle. Again, it's a puzzle. We don't know anything about this. I'll tell you right now. My brain that's looked at some pedigrees in my lifetime, I look at this pedigree and I'm like, oh, affected parents? That is probably a dominant condition. Affected parents who pass on the allele indicate that it's possibly a dominant trait. Should we check and see if it is dominant? Let's go ahead and just do, let's check. Autosomal dominant question mark? Well, we know if it's autosomal dominant, all we know is that there's at least one copy and both parents have at least one copy. Look, if now could both parents be homozygous, dominant, why? What's the genotype of my unaffected kids? Where did those little a's come from? One had to come from sperm parent, one had to come from egg parent. So we know that those parents have to be heterozygous if this is an autosomal dominant condition. We don't know what these guys have going on. Okay, cool. So it could be autosomal dominant. Could it be recessive? Let's just see, I'm gonna leave it on here. Could it be recessive? Could it be autosomal recessive? If it's autosomal recessive, then it's gonna have to be homozygous recessive. Both parents have to be homozygous recessive. And these kids have to be homozygous recessive, but these guys have to have at least one dominant allele. Where would they get it? They can't. So no, it couldn't be autosomal recessive. Does that make sense? Because there's nowhere to get that dominant allele that would make it so you didn't show the condition. All right, we could also check to see if it is, I'm gonna make a case that it couldn't be, I don't know, I guess we could try to see if it's sex-linked recessive, but I can't do it all on the same thing. So say goodbye to these, cut, and now, come back. Okay, let's try ex-linked recessive. This is a question mark, I'm skeptical. If it is ex-linked recessive, then she has to have, I turned it into Bs now, nobody knows why. She has to have two copies of the recessive allele, and he has to have the recessive allele with a Y chromosome. Do you agree that that hat, if they're gonna express it, they have to have those genotypes. And then I go automatically to here, is there any way that those boys could end up with X, big B, Y? No, that cannot happen because there are no big Bs. So no, it is not ex-linked recessive. My intuition at the beginning of this was that if the parents both have it, it's unlikely for it to be a recessive trait. Let's see if it's possible for it to be ex-linked dominant. And I'm gonna do the same thing, I'm gonna erase everything. Ex-linked dominant. You see how this isn't easy, but it's kind of like a puzzle. All right, if it's ex-linked dominant, then this guy has to have it. And he also has to have a Y. She needs one copy of it, an X chromosome with who knows what else. The girls are going to get an X chromosome from their dad. So they're guaranteed to have one X chromosome that has it. And indeed, that is what they show. Their other X chromosome from mom, nobody knows, but nobody cares because they already have it. Is it possible for these boys to get a non-affected X, a recessive X, along with their Y? Do you agree? This means the recessive X has to come from mom. It could happen, huh? It could totally, that could, if she has a recessive X, then this pedigree is possible with ex-linked dominant. Possible. Would it be possible to have an affected boy? Yes. Would it be possible to have an unaffected girl? Ooh, that's a good question. Can we get an unaffected... Girl? I'm gonna say no because no matter what, she's gonna get at least one of her X chromosomes from her dad who has the allele. So she will express it because it's dominant. All right, how you feeling? Dudes, I need water before I start coughing. Which is gonna happen really fast. Okay, good job. Keep studying. Bye-bye.