A couple of exceptions here, genetic mapping, and then some human genetics on Thursday. Alright? I've posted up for you some more detailed learning objectives for each section. Right? So you have these to work through.
So sex linkage, exceptions to make sure that inheritance, and so on. So those are all there. Use those as your guide for what to focus on as you're studying the lecture and the chapter in the textbook. Alright. Chromosomes.
So Mendel did his work long before 1900, as you know, and had no idea about chromosomes, had no idea about DNA, didn't even use the term genes. Right? But he was able to surmise from his very careful work the law of segregation and the law of independent assortment. And as that as his work was rediscovered, started thinking about, well, where do these units of inheritance, these particles of inheritance as as the mammal described out, where do these things exist within living organisms? So there were some ideas that they might be part of the chromosomes because, work, researchers were able to see chromosomes in meiosis pretty early on and start thinking about this idea.
And if, one of the important observations was that similar chromosomes pair with one another during meiosis. And we know that homologous chromosomes are what those similar chromosomes are that come together in paramiosis. So these ideas, had, researchers of the time start to think about, well, maybe those genes are on chromosomes. So how do we know that genes are on chromosomes? Of course, you know that they are.
How do we know that? So let's look at an experiment from Morgan's lab from back in 1910 when Morgan was working with, our favorite fruit fruit fly, Drosophila, and discovered a mutant male fly with white eyes. So here are our wild type normal red eyes on a fruit fly. Here's a male with white eyes. And so after discovering this white eyed male, did a cross to a red eyed female, f one progeny, all have red eyes.
So that tells us that red eyes is the dominant trait. So we're gonna follow some process here in Drosophila. So as we do, let's get Drosophila nomenclature down. So far, we've used capital letters and small letters for dominant and recessive wheels. But when we're doing genetics in Drosophila, we have a very particular type of nomenclature that we use for these genes.
So in this example, w plus is the dominant allele for red eye color. Little w is the recessive allele for white eyes. Hello? K. So what we have is we have a cross between a red eye With a male.
With this white eyed male. Yeah. And in the f one, we get all red eyes. Right? All red.
No white eyed I know. Progeny at all. So far, this looks good. Right? This is what we expect in a monohybrid cross where we have a dominant and a recessive allele.
We might even go as far as break down some genotypes here. Right? So a w plus and a w gives us red eyes on this f one. So far, we're all together. Right?
That simple. Alright. Well, what happens next? You take those f one next? You take those f one females and cross them with some f one males, which is what we did a lot.
Right? This is our f one. So we do, like, a self cross, right, to get to our f 2. And our f 2, we should get a 3 to 1 ratio of red to white eyes. Correct?
Yes, sir. Right. That's what we should expect in a normal monohybrid cross, but that's not what happened. What happened is the f two generation contains individuals with red eyes and with white eyes, but all the white eyed flies were made. That was unexpected.
We should have had a 3 to 1 ratio of red red to white eyes, but in everything we've done so far, there's been no difference between males and females, but we're seeing this difference. Only the males have white eyes. Alright? So our f2 here, we get red eyed females. We get red eyed males.
And white eyed males. So this is unexpected. So one of the things that, Morgan and his group thought about was, well, maybe whatever this allele is that's causing these white eyes in males, maybe it's lethal in females. Maybe it's lethal in females. So they did a cross where they take the parental of a female and one of these f one females and do a cross.
What kind of cross is that? It's a test cross. Right? So we're gonna take our w plus w female. This is one of our f one females.
We're gonna cross it to our w w male, which was one of our the parental males, and see what we get from this cross. So we're doing a test cross here. Right? If everything's all as it should, the proportion of progeny we get from that test cross should be a 1 to 1 ratio, white to red eyes, but we wanna see what happens. Can we get white eyed females from this?
And in fact, we do. Alright. So let me skip this slide for a moment. So when you take do this test cross, you get white eyed males when you do this test cross with an f one female and a white eyed male, we see now white eyed females do survive. It's not fatal.
So we have to rethink what's going on. We have to rethink why in this f 2 we don't get any red eyed females. Well, Morgan knew that there was a difference between the x and the y chromosomes in those fruit flies. So let's back up here a moment. Alright.
Oops. I went forward. Let's back up here. Alright. So Morgan knew that those, x and y chromosomes looked different.
So hypothesized that this I color gene is on the x chromosome. And the y chromosome is much smaller, and it's gonna have a different set of genes than the x chromosome. So if we draw out our crosses with our x chromosome and our y chromosome in our parental male generation, and this x chromosome is colored in white because it's carrying that little w white eye to the male. With our parental female generation, which is w plus w plus, These are her 2 x chromosomes. And we fill in our Punnett square, what we see is all of all the progeny have red eyes, which is what you're gonna get in this cross.
Right? That's the same thing as what I wrote here. F one's all red eye. So what we see is we have females that are heterozygous. We have males that have 1 x chromosome with that red allele and one y chromosome.
Everybody has red eyes. So this is so far consistent with what we observed with this hypothesis. Alright? Now if we take one of these f one males, note the f one males have an x chromosome with the red allele and a y chromosome, We cross it to one of these f one females, which are heterozygous. That's what we see here.
In this slide, here's our f one male with its x chromosome with the red allele, its y chromosome. There's an x chromosome with a red allele, an x chromosome with the white allele. We see that we have only males that are gonna show those white eyes because this heterozygous female here is gonna show red eyes. Eyes. So it's not that there's something lethal for this allele in females, it's that this allele is carried on the X chromosome.
So this accounts for what we see here, red eyed females, red eyed males, and white eyed males, but no white eyed females. K? Alright. So we can represent these with these pictures of chromosomes colored in for the eye color, but we can represent these another way. So I wrote down these genotypes here using appropriate Drosophila notation, and you should be able to use appropriate Drosophila notation.
W plus is the dominant red eye allele. W is the recessive white eye allele. But these are carried on the x chromosome. So over here, what I'm gonna do is I'm gonna change what I wrote down in our parental graphs. I'm gonna write down x with a superscript w plus.
Alright. Over here, I'm gonna write an x with a little w and a y. Right. These males only have one allele for I because it's carried on that x chromosome. So when we do this, if we come back over here to our test cross, what we're doing in our test cross is we have an x chromosome with the w plus allele, an x chromosome with a w allele, and this f one female.
Right? These f one females have to be heterozygous. We're crossing that with this male that from the parental generation that has white eyes, they are x w y. Right? They only have one allele for eye color.
So if we fill in our Punnett square for this, we get x will work for you. W plus x w from the female. From the male, we get x wy. So x w x w x w w, x w, x w, x w, x w, x w, x w, x w, x w, x w, x w, x w, x w, x w, x w, x w, x w, x w, x w, x w, x w, x w, x w, x w, x w, x w, x w, y. So we have red eyed females, white eyed females, red eyed males, red eyed males, and white eyed males.
So our test cross is still a 1 to 1 ratio as it should be, and it works out that we can see that those white eyes can indeed be expressed in females. It does not equal to females. So this experiment was a really good demonstration that genes are on chromosomes because we could sort out what was going on on the X chromosome in these various crosses. So from this, we know genes are carried on chromosomes. K?
So if we jump ahead here, Morgan concluded that this I colored gene resides on the X chromosome, and that traits determined by genes on X chromosomes are now called sex linked traits. Right? Those X linked traits or sex linked traits are the ones on sex chromosomes. So if we, skip ahead here to this figure from your textbook, this is the same process before, but I took out these yellow boxes before I got to this point. What we can see is both X chromosomes in that parental generation have the allele for red eyes.
Right? That's what we wrote down right here in our parental generation. Our parental male generation, we have an x with the white eye allele and a y chromosome. K? So we can see that this is indeed a sex linked tree.
We can account for the patterns that, Morgan and his team saw when they were working with this particular cross of the cell. Alright. So far so good? Have I convinced you that genes are on chromosomes? Chromosomes, or are you just ready to accept it because you know it's true?
Alright. Alright. So this is a figure. I'm not gonna go through this figure, but I put this one up here for you guys. I took this from a different textbook, and what it does is it's not exactly the same experiment that we saw in Morgan, but it sets up what's called a reciprocal cross.
So here, our first cross is our red eyed female crossed with our white eyed male, and you can follow through and see the project. And we did this early cross. Over here, we're doing a cross with a homozygous white eyed female and a red eyed male. And you'll see the proportion of progeny that you get down here is different in this reciprocal cross. So I suggest that you guys go to this figure, work through this, and make sure you can track the chromosomes and the alleles, and that that reciprocal cross, the difference you get makes sense.
Okay? So it's a good practice problem for you guys to walk through. This column is exactly what we just did. This one, we didn't do. Instead of this, we did our test cross.
Okay? Alright. So work through that slide that's up there, with the ones on Canvas for you guys. Okay? Alright.
If it's not in Canvas, let me know, and I'll add it. Alright? Cool. Alright. So what do we know about these sex chromosomes?
We'll pause for a moment and learn a little bit more about that. So they are a pair of chromosomes that are dissimilar, obviously. Right? But they pair together in meiosis and mitosis. So the sex chromosomes are not homologous.
They don't have the homologous genes along their length as all of our other homologous pairs do, but those sex chromosomes do pair with each other during meiosis and mitosis. So an x and a y chromosome are gonna pair for meiosis. K? And sex determination in drosophila is based on what we call the x y system, and it's based on the number of x chromosomes. So 2 x chromosomes gives us a female fly.
One x and one y gives us a male fly. There are different kinds of of chromosomal pairs in terms of sex determination. But this pairing is, very common. Right? Same in humans.
Right? We have 2 x chromosomes as a female. Having a y chromosome, and this x y pair leads to maleness. In birds, we have something a little different. The sex chromosomes in birds are z and w.
Right? So z 2 z chromosomes is male, and females are z w. So that's a little different because the females are the ones that we have, the non homologous pair paired in birds. And some insects have some different sex determination set systems. Two x's are female, an x and an o, meaning there's not a second chromosome.
Alright? So there's a table here that summarizes that. So a human, a Drosophila, x x and x y. Birds, z w z z. Grass hoppers, x x are female, x o are male.
And then in honeybees, diploid individuals are female and half way individuals are male. K? So lots of different ways to determine, sex across the animal kingdom. Okay. Now in humans, as you well know, we have 46 total chromosomes, 23 pairs.
22 of those pairs are autosomes, and then the other pair are the sex chromosomes. So 22 autosomes, 22 pairs of autosomes plus then the sex chromosomes. The y chromosome is smaller than the x chromosome. It's highly condensed. It doesn't have very many genes on it, but those genes are really critical.
In humans, the default is female. The SRI gene, which is found on the y chromosome, is expressed and then that dictates development of maleness. Okay? So x y leads to males and humans. Now there are consequences of this for traits that are inherited that are on where the, genes for those traits reside on the x chromosome.
Right? We just saw there are consequences in terms of, the phenotypes here for those genes on those x chromosomes. Notice that in our Drosophila, this original fly that had these white eyes had this recessive allele on its x chromosome that led to white eyes. It only has one x chromosome, so only one allele is determining that phenotype. Right?
So you see this recessive phenotype showing up here. In the heterozygous female, we see red eyes. Right? When you start thinking about, genes and their alleles that are carried on those x chromosomes, what we see is that there are certain, genetic diseases or disorders or phenotypes, whatever word you wanna use, that affect males to a greater degree than females as a result of being, carried on the x chromosome. Many of these, situations are due to recessive alleles.
Males only have 1 x chromosome, and so we're likely to see those recessive traits. Right? We only have 1 x chromosome. So these x linked recessive alleles, there are many of them. Just two examples here for you now.
We'll see more on Wednesday or I'm sorry, on Thursday. So color blindness is an x linked recessive allele. Hemophilia is an x linked recessive allele, and we'll see some additional ones in class when we look at some human genetics on Thursday. So there are consequences for, what we see in terms of traits when those genes are carried on that x chromosome. Okay?
Or they are sex linked genes is typically how we describe them. Okay? Cool. So far so good. Alright.
Now here's here's a puzzle, though. Female Drosophila, as in female humans, have 2 X chromosomes, and males only have 1. Chromosomes and males only have 1. One x chromosome is enough. Right?
One dose of those alleles on that x chromosome are sufficient. So if we think about females as x x, males as x y, females have a double dose of these genes that are carried on the x chromosome. Half of that dose is enough. You only need 1. So what we see in mammals is something called dosage compensation because you only need one copy of the x chromosome to have the right amount of all of the gene products for the genes on that x chromosome, you see this process where one of those x chromosomes is inactivated.
And it's inactivated, at during a stage, during embryonic development where the one x chromosome gets condensed into this structure that's called a bar body. So you have you're at a point where you have an embryo that is a multicellular embryo. And in all of those cells in a female embryo, there are 2 X chromosomes, but one of them gets inactivated. It's totally random which one gets inactivated. So if there were some way to tell the difference between those two X chromosomes, in about half of those cells, one of them would be inactivated, and the rest of those cells, the other one would be.
So there's this inactivation of one of these X chromosomes at an embryonic stage where you have multiple cells. It's random which one is inactivated, but then every daughter cell from those after that maintains that inactivation. Right? So what we need is a way to tell those X chromosomes from each other so that we can see sort of this pattern of X inactivation. Right?
And this dosage compensation. And we can see that in a really interesting way in the phenotype of what's called the calico cat. So if we have these x chromosomes and they have different genes for some trait I'm sorry, different alleles along them, and we can tell one from the other, we can see that a female mammal is a mosaic. Half of her cells have 1 x chromosome inactivated, the other half have the other one inactivated. That was a random event.
And in calico cats, we see this in this black and orange pattern of their fur. So there are 2 alleles of genes on the x chromosome that determine fur color. Color. There's an allele for black and there's an allele for orange. And in some of the cat cells, the orange allele remains act on that x chromosome that's active, and the black allele has been inactivated in this condensed X chromosome that has this bar body, so you get an orange patch.
In other cells, the orange allele is on the X chromosome that's been inactivated in the bar body, and you get, but the black allele is on the active x chromosome, so you get these black spots. K? So this is a mosaic where some cells are expressing the orange allele. Some cells are expressing the black. We can see this for other types of phenotypes too.
Right? So hey. Hey, you guys up in the balcony right there in that crew blue t shirt. I think that's where the noise is coming from. So if it's not you, I'm sorry.
If it's your neighbors, ask them to be quiet. Alright. Thanks. Alright. So we can see, this sort of hybrid I'm sorry.
This in other, traits as well. So in humans, there's a condition, where there's a recessive allele on the x chromosome that prevents formation of sweat glands in the skin. So there are individuals who have patches of skin with sweat glands and patches of skin without sweat glands, similar to the patches of blue and orange fur that we see here in these calyx cats. Okay? Now the one thing about this that adds a little layer of complexity is there is another gene involved in determining hook color on a separate autosome, not on the x chromosome, on a separate autosome that, is involved in whether or not I'm sorry.
It is on the X chromosome. It's not on an autosome. That involves whether or not the, fur is laid down in the skin cells, so that's why you get all this white. So this calico cat has a lot of weight. Sometimes you see a calico cat with very little weight.
So there's a whole other gene that's also involved that we're leaning out here. But we can see the mosaicism for the brown, the black, and the orange. So can male cats show this pattern? We see some nose. Male cats show this mosaic pattern expression.
They cannot. They have only 1 x chromosome. So what we see is male cats have only 1 x, so they are either all orange or all black. You don't see these patches of all color types. Alright.
Cool. Now there are some exceptions to the chromosome theory of inheritance in terms of, phenotypes that we can see and how they are inherited because we know that there are some genes that are not on chromosomes in eukaryotic cells. Right? There are genes that are not on the chromosomes because there are genes that are within the genomes of the mitochondria and the chloroplasts. So there are mitochondrial genes and there are chloroplast genes, and their pattern of inheritance doesn't follow where chromosomes end up at the end of meiosis.
Right? Those genes that are in mitochondria and chloroplasts don't undergo meiosis. Those mitochondria and chloroplasts do get divided into cells at the end of meiosis, but not they are not sorted in the way that the homologous chromosomes are. So there are some traits that we see that don't look like genes are on chromosomes. But they are on chromosomes.
They're just on the genomes within the mitochondria and the chloroplasts. So genes from the mitochondria and the chloroplasts are often passed by only one parent. For mitochondrial inheritance, we see this in humans and it's often called maternal inheritance because the mitochondria genes that get passed on to the next generation come the female parent. So we see maternal inheritance, for traits that are carried on those mitochondrial genes. K?
And we'll see an example of one of those on Thursday as well. Alright. So what else? So, you know, we we now know that these genes are in some position. They are on these chromosomes.
How can we take advantage of this? Well, early on, understanding that genes are in a physical position on a chromosome, we can say, you know what? Maybe we can map a chromosome. Maybe we can draw a map and say this gene is in this place on this chromosome, and that gene is on that place on that chromosome. So thinking about being able to draw max is really important, and we need to point to infer the distance between those genes.
It turns out that we can make those distance estimates based on patterns of genetic recombination. When we learned about meiosis, one of the really important things that happens in in, prophase 1 is those tetrads come together and make, chiasma into crossing over. That crossing over in meiosis 1 is recombination. Right? That crossing over is recombination.
So if a crossover occurs, parental alleles are recombined producing recombinant individuals. And we'll see how that works as and how we can use that as we move forward. So here's a diagram of some chromosomes of some unknown diploid organism. And when we look at these chromosomes, they have this nice color coding here so we can keep track of what's going on. So in our parent generation, we have a parent who is homozygous for both, little a and little b.
So here are that parent's chromosomes, and we're putting the little a and the little b alleles on the same chromosome. Right? So this is homozygous little a, little a, little b, little b. The other parent is homozygous capital a, capital a, and capital b, capital b. And we've placed those on positions on those chromosomes.
So, of course, in our f one generation, we get the heterozygous. And if we're tracking those alleles by where they reside on those chromosomes, we have one chromosome with the little a, little b that came from one parent. The other chromosome has the capital a and the capital b from the other parent. Alright? So here's our heterozygous.
If we have a normal meiosis with no crossing over, we know from this that we can make 4 types of gametes. Right? And we've done that in our planet squares. So let's write down our gametes that we're gonna get from this. Alright.
So let's let the chalk over here. So what we would write down without drawing the chromosomes, we have capital a, capital b, and little a, little b. Right? This is our f one individual. And if we're going to do a cross and we're going to write down the gametes from this individual, we're going to write down that we're going to get a gamete that has the capital a and the capital b allele together.
Right? We're going to write down we're going to get a gamete that has a capital a, little b a little together, a little a and a capital b, and a little a and a little b. Right? We can get 4 types of gametes here. But in fact, if these genes are linked, meaning that they're on the same chromosomes, if we have meiosis without crossing over, we only get 2 types of gametes from this f one individual.
We get gametes with the little a and and the little b together. We can get 2 of those. We get gametes with the capital a and the capital b together. And we say that these are all parental combinations. Right?
It's the parents to get to this f f one individual or this. So this is our p, our parental generation. Here's our f one. Here are the gametes we get if those genes are unlinked, meaning not on the same chromosome. But if they're on the same chromosome and there's no crossing over, we only get this one and this one.
Right? The other 2 are new combinations of those alleles that were not present in the parental generation. These 2, we're only gonna get if it's a crossing over event. These 2 are the recombinants. K.
Those 2 are the recombinant lengths. And we can see here if we have meiosis with crossing over, here's prophase 1 where these homologous chromosomes, these sister chromatids. See how they're crossed over with each other here? We have breaking and rejoining. So this sister chromatid here has a little a with a capital b.
This chromatid has a capital a with a little b. And when we separate those with meiosis 2, we get 4 types of gametes, the recombinant and the parentals. The recombinant in the middle here and the parentals. We only get those if there's a recombination event in between. Alright?
So far so good? Yeah? You one of the key pieces here is you're thinking about, you know, what kinds of questions are you going to have to solve and what kinds of questions are you gonna have to answer. You need to know what is parental and what is recombinant. Right?
Parental combinations of these alleles, recombinant combinations of those alleles. I can ask that as a question. I can give you some data, but you need to tell those apart. Question. So over here?
Yes. They did. There was no crossing over there. There's not always gonna be recombination between them. Okay.
Okay? So this is what you get without a crossover. This is what you get if there is a crossover. Okay? And we'll come back to that.
You can end up keeping these parental classes for some interesting reasons as we can see here. Okay? But for right now, we when you have a crossover, you get a new combination or recombinant combination of those alleles that wasn't present in the parental generation. So we're telling the parentals from the recombinant classes so far. K.
Alright. Cool. Good. Good. Good.
Alright. So one of the interesting things is that, Barbara McClintock, who is just a I don't know. There's so many words I could use. Freaking genius, actually, is what I might say. Did this experiment that actually demonstrated that crossing over happens and genes are really nonchromosomes.
We're working with a research partner. They set up a cross where they were able to construct a chromosome that they could see in the under the microscope and identify by adding an extension to one end and another structure they called the knob to the other end. So they did this cross in corn where they were looking at 2 alleles, one that was colored and one that determined the texture of, the kernel texture of the kernel, so it was colored and spartchy. So we have the recessive little c allele here with the dominant waxy allele here. We have the dominant c allele with the here.
And what they were able to do was in, doing these crosses, were able to see the recombinant gametes and then look the recombinant phenotypes, then look under the microscope and actually see the chromosome structures had changed. So they could demonstrate that there was physical exchange of information between these chromosomes because they could look at them under the microscope and say, hey. This one where this, recessive waxy allele was used to be on the chromosome with the knob and the extension. Now it only has the extension and the knob is on the other one. So they can demonstrate actual physical exchange of material and meiosis in producing these new recombinant traits.
So it's a really pretty cool experiment. So here we're looking at the test cross, that you can do once you have these, heterozygous individuals and make the prediction of what you're gonna get from there. So it's a really cool experiment, and I think it's one of these ones that you look at it now and you're like, oh, yeah. I see the colored dots moving around and stuff. But I think it's one you have to look at for a little bit to really see what's going on.
So I want you guys to take a little time and look this over and make sure you really see what's going on in this experiment. That this really does demonstrate physical exchange of pieces of chromosomes with each other because that's what it's really about. We know we get this recombination happening. We can actually see that physical exchange in this particular experiment. Alright.
Cool. So far so good. Alright. So, they see the physical exchange of genetic material with genetic recombination. Now the other thing, that started this whole discussion, once we know that genes are on chromosomes, can we use that information and make maps?
Can we map the physical locations of genes along chromosomes? So this is what we wanna do, and, Morgan's lab starts working on this and looking at the physical distance along a chromosome. And so, before we come back to these bullet point conclusions here, let's look at an example. Why are we not moving forward? Alright.
Alright. So we're gonna test this idea that the distance between genes is proportional to the recombination frequency between those solvials. But I think what we'll do before we look at, Morgan's experiment is let's do our own. So you have a problem in front of you. Alright?
Where the question is, are these genes linked or not? Alright? So in Drosophila, a gene determines body color. Dominant wild type allele of this gene produces gray body. The recessive allele produces a yellow body.
Another gene that this off road determines wing gene. The wild type normal wing is dominant to mini wings. So a female that's true breeding gray body normal wings is mated with a male that has yellow body mini wings. And then the f one females are crossed back in a test cross, and then these are the projects. So this is what we wanna do.
First of all, write down using appropriate trussock and plumbing culture some symbols for the genotypes of the flies in the thoracic generation and in the f one generation. And then together, we'll work through that test results. Okay? So your first question, are they linked or unlinked? But in addition to that, let's write down some things about those flies, right, using the correct nomenclature so that we can work through this.
And I would put this up here if I could. K. If you does anyone need a copy of the trial holder? Copy. Yes?
If you need a copy, hold up your hand. We got some coming around. Alright. So our first order of business is let's figure out the genotypes. We have a female that's true breeding gray normal wings, mated with a male that has a yellow body and mini wings.
We get some genotype symbols for those. Let's see what we got in our It's a list. K. Using correct Drosophila nomenclature. What symbols are you getting?
So talk to your neighbors. Work that out. Let's see what you have. Write down those genotypes. Yeah.
Wait a minute. We have b plus b plus. How are we doing? Doing alright. It's going.
The tension. It's going. The tension just needs to be in the case. Just turn the phone down, shake. Alright.
Hey, guys. Let's let's pause for a moment. Okay. I'm seeing lots and lots of symbols out there. So let's come back and think about the symbols for just a moment.
Alright? We'll leave that there. One of the things that I wanna note is that genes are carried on all the chromosomes, not just the x chromosome. In this particular problem that we're working out right here, I'm gonna tell you right now, this is not an x linked trait. So you don't have to make note like I did in this problem of the x chromosome.
Right? These genes are on an autosome, not on the exocrine. They're on the autosomes. So we have, gray body is dominant to yellow body. For eye color, we use the little w for white eyes and w plus for the dominant red eyes.
So here what you want to do is you want to use the little y as the recessive allele for yellow body, and y plus is the dominant allele that's gonna give you a gray body. K? That would be the appropriate kind of Drosophila nomenclature. Then we also have normal wings and mini wings, and you know that normal wings is dominant to mini wings. So here you could go a lot of different ways.
What I did is I used MW and MW plus. So MW, I'm using two letters for one allele here. Right? MW stands for the recessive allele, that when it's homozygous, you get mini wings. M w superscript plus is the dominant allele that you get normal wings.
K? So that would be the appropriate kind of Drosophila nomenclature I want you to use when you're looking at this kind of problem. Right? So far so good. So, write down so I I haven't looked at anybody's crosses yet.
Let's write let's answer a couple questions. Yeah. Yeah. That is the Drosophila nomenclature process. So not that's not true in other organisms.
But if you are a Drosophila geneticist, you're gonna pick a symbol after your recessive tree. I don't think you'd make a w because it's yellow. You use y. Right? So you wanna use a letter that's gonna help you later when you fill in your Punnett square figure out your genotypes.
So you could define it different ways, but I would use y and y plus. Yeah. Way in the back, and then I'll come up. If you were doing, across in pea plants, you would use big y small y. But if you're working in a lab that uses Drosophila as their genetic organism, you know, their model system, you're gonna use a little y with a plus for the dominant allele.
K? Okay? So we're gonna try and use the Dersophila nomenclature here. Our dominant allele is little y with a superscript plus. That gives you a gray body.
Okay? Alright? So let's try and work it out. Yeah. One more question.
Apparently, it's this. It's by convention, it's lowercase. Okay? Yeah. One more.
So the plus, this is the recessive allele that in the homo homozygous condition gives you a yellow body. The plus is an allele for that same body color t, but it's the dominant allele, it's gonna give you the gray body. Okay? So the plus is telling you that's the dominant allele. These are remember, these are alleles of the same gene for the trait body color.
Okay? There are more So use the same letter for them, but you have to indicate one is dominant. K? Okay. So write out let's go on.
Let's write out your parental genotypes, your f one genotype. And if you want to then do your test cross and write out all that, go ahead. But let's first get through the parental and the f one. No. This is the Alright.
Let's see what you have for parental and the f one. So I'm gonna turn off my You combine as a switch? Yeah. This is 1 g. Yes.
We are setting the combination of the opposite. I'm setting the combination of the opposite. Yeah. The opposite. And the parents are.
These have too. So, yeah, let's just do it. You guys got it? Are you are you ready to work it out? Work it out?
Yeah. Yeah. Alright. How are we doing? Are you done, or you want one more minute?
One more minute. Okay. Keep working. Keep working. I had a whole a whole bunch of Yeah.
I got a person. Pretty soon that, whichever thing Yes, professor Rubio. I am so on task for her. I'm considering the recombination of jeans. Alright.
Let's see what you got. Alright, guys. Let's see what's going on. So I wrote down how I'm gonna write my genotypes for the parental generation. So we have true breeding flies.
Stating that they're true breeding is gonna tell you that they're homozygous. Right? They're gonna be homozygous for the alleles for the traits of interest. That's why I told you they're true. So we have one pair that is gonna be a gray bodied, normal winged fly.
It's true breeding. So it's homozygous for y plus y plus. That's why it has the gray body. And it's homozygous for m w plus, m w plus. That's why it has normal wings.
The other fly we're crossing this with has a yellow body, so it's homozygous little y little y. And it has many wings, So it's m w m w homozygous for that trait. Right? So what's the genotype in our f one? I didn't know that.
Heterozygous. Yes. It's It's heterozygous for both of these alleles. Right? It's it's just like what we did in the blue plants but with different centers.
Right? So the same idea. So we get a y plus y. Right? We get a y plus from here, a y from here.
I know. We get an m w plus from there, and an m w from here. And what is the phenotype? What's that? Gray body.
1, 2, this. With what kind of wings? Normal. Normal wings. Right?
So this is our heterozygote is gray normal. I no. I mean, what if there's more than This is our f one generation. Like states. All of our f one flies look like this.
That makes sense. So now we're gonna take It's impossible. One of these f one females and do a test cross. So let's come over here. Our f one female is y plus y, m w plus m w.
We're gonna do a test cross. So what's the genotype of the male we're gonna cross this file with? Yeah. What if there's multiple? It's like, oh.
So homozygous recessive for both. Right? A test cross is defined as crossing an individual that shows dominant phenotype. These are the dominant phenotypes here. We're taking this individual with that dominant phenotype and crossing it with an individual that has the recessive phenotype.
So this is going to be a fly that has a yellow body and many wings. So it's homozygous for both of those. So in this test cross, we can write out our Punnett square. And so over here, we're we can get y plus with m w plus as a Gammie. We can get an I plus with m w.
We can get little y with m w plus, and we can get little y with mw. Right? Those are the gametes from our heterozygous individual. And then from our homozygous individual, we really only get one type of gamete. So I could write it down 4 times, but I'm lazy.
So I'm just gonna write it once. Right? This homozygous recessive individual can only make gametes that have those homozygous. I'm sorry. That have those recessable units.
Right? So you get one type of gamete, and then you can fill this in. So let's fill it in. We have y plus y, m w plus m w. Yeah.
Absolutely. We have y plus y, m w, m w. We have y y m w plus m w, and we have y y m w m w. And these are going to be different phenotypes. So now we have to write in what are the phenotypes that we have here.
So our top line, what is this phenotype? Gray body, normal wings. Right? Y plus is gray body, m w plus is normal wings. So this is gray, normal.
We'll just write that down. Right? Gray normal. What's the next one? Gray mini.
And this one's gonna be yellow normal. This one is gonna be yellow mini. Right? These are our 4 phenotypes. And in a test cross, we expect a 1 to 1 to 1 to 1 ratio of these.
Right? Now look at the data. Did we get a 1 to 1 to 1 ratio of those? Not at all. Right?
So we got 274 gray normal, 254 yellow mini, then 3834 of our other phenotypic classes. Right? Which of our 4 phenotypic classes are the parental phenotypic classes? So if we go all the way back here, the parental combination was gray normal and yellow mini. So gray normal, this one is parental, and yellow mini, this one is parental.
These 2 are new combinations between body color and wing type. Right? They're the recombinants. Now if we look at our data table, which classes do we have the most of? The biggest numbers go with which classes?
We have 274 gray normal. Right? 274 of these guys. And how many yellow mini? 258 something.
I don't know. Is that the number? 54. Okay. Right?
The parental classes are occurring much more frequently than our test cross would predict. Right? The recombinant classes, these new combinations are occurring much less frequently. That's telling us that indeed these genes are linked, and they are so they are on the same chromosome. Right?
Most often during meiosis, they are not assorting independently from each other. The gene for body color is not assorting independently for the gene for wing shape here because they are on the same chromosome. That's why these phenotypic classes are in such a larger number compared to the recombinant ones. What we can do is we can take advantage of the fact that we know how many of these recombinant ones, and we can calculate something called recombination frequency. Right?
And so our recombination frequency is a pretty simple calculation. It's the number of recombinants, 38 +34 divided by the total. Here is the mistake that I see all the time in calculating recombination frequency. Instead of dividing by the total, people divide by the parentals. That is the wrong number.
It's 38 +34 divided by I think this comes out to 600. Is that right? Yeah. The total here is 600. So you're gonna divide this by 600 times 100 and get our recombination frequency.
K? So what does that come out to be? 12%. Alright? Hell, yes.
That's how you calculate the recombination frequency. So you guys can bet. I'm gonna give you a multiple choice question. Right? Give you a bunch of numbers and say, what is the recombination frequency?
And you're gonna have to pick the one with the right recombination frequency. 1 of the wrong ones is going to be recombinanced divided by parentals. The correct answer is going to be recombinanced divided by the total. Don't get that one wrong. The answer's a okay.
Okay? Recombidence divided by total. What it divide it by 12. What it gives? Yeah.
So so then you'll understand the question. You don't worry. Yeah. Don't worry. Alright.
Yeah. If I give you a set of progeny like this, I give you 4 classes of progeny with the number of each and say what is the recombination frequency? That is the calculation that you do. That's what I'm talking about. But do not divide it by the commonest divided by total.
Yes. Question. So the term is the state, they are linked and then it's all They are. Yes. That's what linked means, because they are physically on those same chromosomes.
They are physically linked together. You only get those recombinant classes when during prophase one amiosis, you have a crossing over event and those chromosomes trade pieces of each other. K? Question over here. Correct.
In a test process, if the genes are unlinked, you should get an equal amount of all 4 of those phenotypic classes. Right? You guys recall last Thursday, we did test process in other types of organisms because you can determine the genotype of an individual of unknown phenotype by doing a test cross, and you get that 1 to 1 to 1 to 1 ratio in that test frost, but only if they're unlinked. Yes. Way in the back.
If they were what? If they were linked and there was no crossing over during meiosis, there would be 0 recombinant. But your question is an interesting one. We got a 12% recombination frequency here. As the genes get closer and closer together, that recombination frequency gets smaller and smaller and smaller because you're less likely to have a crossing over and then between them.
So you get farther apart, the recombination frequency gets bigger and bigger. Right? So we know that the genes are linked, and we know that crossing over happens in meiosis to give us these recombinants. Okay? Cool?
Does that answer your question? Okay. Cool. Sort of. Alright.
Alright. Cool. So far so good? Yeah? Yeah?
Alright. So I think you have everything we need on your note card. So let's pass those in, and then I just have a few more things to say about this property. Alright? Yes.
Don't worry. On your go cards, you need your name, network ID, today's date, and we'll be good to go. K? Pass them. Where's this is?
It it's okay. If you did the work on your worksheet, just keep it. Just write it stock. Card ID, your name, your network ID. Just write the jeans are, which is the minor jeans are Jean's are black.
Pass it over and you get credit. Okay? So pass your notecards over and you'll get credit. So we'll collect those now. Pass them to the end of the program before we collect them.
Alright? Numbers. Write down. Yes. Teens are linked.
Then I have a few more comments about this problem. We have a little ways to go. We're not quite done. Okay? Pass your no cards.
We're not quite done. Alright. Stephanie or the no part. Theresa. Has everyone passed in their no part?
Yes? Alright. So I want alright, guys. Got no cards passed in. We have one more piece of this.
And it's gonna come back to this question about what would we get if they were unlanked? What would they get if they were unlanked? Right? You got all the note cards? Cool.
Alright. Excellent. Okay. So we have 600 total progeny. If these genes were unlanked, how many would you predict should be in each phenotypic class?
What's that? How many should be in each phenotypic class that are unlinked? 150? Yes. Exactly right.
If those genes were unlinked, you should get an equal amount of each of them. Right? You should get 150, 150, 150, 150. Our actual experimental results deviate very far from that, right? Because we have 274, 254, 38, and whatever that other number was.
Right? So we're deviating very far from what we would expect. So this is really good evidence that these genes are residing in the same chromosome. K? Don't get the predictable ratio before unlike here.
So that's critical. Now let me let me ask you this question. Let's calculate the recombination frequency if we have 150 of each of them. Let's stick with this as the recombinant class and not the recombinant class. So we're gonna have 150 +150 divided by 600 times 100.
What do we get? 50%. 50%. 50%. 50%.
That's good, you guys. That's a good question. You say it. Why? So here's the deal.
As the genes get further and further apart on the chromosome, it's much more likely that there's gonna be a recombination frequency or a recombination event between them during miosis. And so what we see is that the maximum recombination frequency we can measure between genes is 50%. Because once you get there, they look unlikely. This is just one sentence. So the percentage is not exactly physical distance, but it gives us a relationship of where genes are along chromosomes.
We draw maps of chromosomes all the time that show distances of, you know, 10 map units. That's just 10%. We can convert it to 10 centiporecants. We call those map units. We show map units of 67 centiporecants.
We can't measure that directly between those genes, but we go map along the chromosome and map them relative to other genes. So you cannot determine, distance between genes once your recombination frequency hits 50% because it looks like they're on different chromosomes. K? So we'll stop there. Yeah.
We'll pick this up with