Okay, so now I want to give you an example that you're going to read about a lot in your book and you're going to see this in lecture and see this is lab. If you have a lab and you're just gonna have to know it. So I suggest you got to just memorize this cross because you will be tested on it, I guarantee. And this has to do with X. Linkage and eye colors and the fly Drosophila. So these are fruit flies and I have very clearly written out what these crosses are and what your professor is talking about in case they're not explained very well. So generally what these crosses are done is to look at X linkage. So this is an X linked trait meaning that the mutation is on the X chromosome and therefore will be inherited differently in males and females. So first we're dealing with the parental trait. And so this is going to be a red eyed female. Let me color these red eyes here. And a white eyed male and I have given you the genotype. And the reason I've given you this is so that you understand that this is that red is dominant and white is the movement. Now, remember how you write these? Is that the plus sign represents what wild type? Right? Remember wild type and the absence of a plus side equals. Mean, now we're dealing with this on the X chromosome. So in females you're going to see two alleles. So you'll see two Ws. And females draw a line here. But you always see one W And one Y. And males. And this is because the males only have one, they have a Y. Chromosome and an X. Whereas females have two X. Is. So when we look at our parental, what you can see here is that the red eyed female that were crossing has 212 wild type alleles. And the white I mail. We're crossing has one mutant and one Y. So to get the F1 generation, if we were to make a Punnett Square, I'm just gonna draw one out here. How would we do this using the parental, we take one allele from the mother or the female and one for the mail for each column. So we would get for the female and we would get the mutant allele and the wide chromosome for the male. So then if you cross these, you get, sorry, this is supposed to be W. W. Let me move out of the way. Okay, so that's what you get. If you do the punnett square. Now, what does this say? Well, first we have these half are female and these have our mail. Now, if I were to ask the question, how many are wild type and or how many present wild type red eyes and how many percent white? You would ask. Okay. Do any of them have pluses? Well, here's a plus, here's a plus, here's a plus and here's a plus. So all of them are this phenotype. So even though there's red or even though there's males and females, all of them have red eyes because all of them have a wild type allele. Now. Generally what happens here is you cross the F one. So yeah and their siblings, but it's flies. So it doesn't matter. So you take a red eyed female F one and made it with its brother, then you look at the F two. So if we were to do this punnett square, what would that look like? You see genetics is a lot of pundits squares. So we have female and male. and so our two alleles would be right. So if we were to do the planet square here, what do we get to get half female half male? And we know this because the presence of the why? And we get 3/4 that look like wild type because each one of these has a plus and this one doesn't it's sad, it's immuned. So we have 3/4 red eyes, males and females and 1/4 wide eyed males only males. Because remember here are the females, they both have a X chromosome that is has the normal Alil and this one only has one chromosome. So it only has half the chance of getting that normally. Well and so it did not and therefore is now sad and it's a mutant. So this is the first cross and this is the cross starting with the red eyed female and the white eyed male and understanding what the parental czar are super important because you can do what's called a reciprocal cross which is we're going to do that next and that is when you take the opposite sexes. So now we're dealing with a red eyed male and a white eyed female. This is a very different cross and it's going to get completely different results. So when you're asked about these crosses on your exam, you need to make sure you understand which crosses it. Talking about it. Talking about the red eyed or the wide eyed female or the wide eyed male because you're gonna get different results. So let's walk through this cross. So now this cross is very different. This is the parental still we're looking at the red eyed male and the white eyed female. So first thing you wanna do is do the punnett square. They can draw it right there we go. So here's our punnett square. So we're going to take the mail which is still going to be down here. Why? And the female which is mutant so it lacks no Plus plus equals wild type absence of plus equals mutant. So when we do these crosses, what we get is you still get females still get males but you'll notice that only the females end up red eyed, that all of the males that are produced end up white eyed. So here's the red eyed females and this is very different. You remember the other cross it was everything was red. This cross you get one half to one half then you can do the F. To the F. To generally is you can do this a bunch of different ways. Well actually no you either cross, you have to cross the red eyed female with a wide eyed male. Again. So we're doing this planet cross. Lots of planet crosses what you get. Actually let me make that bigger. So I don't have to be that horrible person who scrunches up her riding and then you can't read it. So again hopefully you're getting your squares down and you understand where I'm getting these from. These are again wanna leo from each, this is the mother here, this is the father here and you do this cross. Yeah. Mhm. Um So you get males, you get females and um what do you end up with, you end up with one half red eyed females or males right? Because you can get here's the red eye and then here is the white eyed and you have both males and females. And here are the different genotype for them. I get it can be confusing because when we dealt with two crosses here, the reciprocal als one where the parental male would have red eyes and one where the parental female have red eyes. That can be confusing and then the F. One and F two generations are different But if you understand these punnett squares every single time I did one, if you understand where these are coming from, which I wrote them here for you and you understand you know that these are males because they have the Y and these are females, they have two Ws. And you understand that the plus is going to be the wild type which in this case will be red and the absence of the plus will be immuned this case. White. Then you can pretty much answer any question that you may be given about this cross. So hopefully that's clear. I understand it could be a little confusing dealing with these crosses. But hopefully if you want to look back at this, just review it anytime you know your professors talking about it or you may have a quiz question about it. This is a good review because it deals with every has every generation. It has every genotype it has every phenotype. So hopefully that's clear with that. Let's not move on.