Mendel's Experiments and Laws

Hi in this video, we're gonna be talking about Mendel's experiments and laws. Okay so Mendel is Gregor Mendel, he was an Austrian monk and he studied genetics and is really mainly the founder of genetics. Um And his main focus for p plants. Um And the reason he chose pea plants was because you can breed them, you can read a lot of them, you can read them easily. But also there were a lot of pure lines available. So what is a pure line up your line is going to be um when all of the offspring from that line produces another pure line. So that means that the trait that you're looking for will be identical in the parent and in the offspring. And so for instance a yellow seated pure line will produce yellow seated offspring if you know if they're made it together. So if you made a yellow seated pure line with another yellow seated pure line, it's going to produce yellow seated offspring. And so that was a major reason why Mendel chose p plants. Um Because you can, you know, you know what your offspring is going to be if you use these combinations. And so that allowed him to make combinations of pure lines to see what happened. And he was very meticulous when doing these studies. And he labeled each generation in a very specific way. And it's important that you understand what these terms and these labels mean because this is how you're gonna understand everything in genetics from now on. So the first is the parental generation. And this is the first mating that occurs the very first one, male and female or plant another plant. This is what happens. The offspring of that mating is the first filial generation or F. One, which is what you'll pretty much always see it as F. One. And this is the offspring produced from the parental mating. Now when you have an F. One generation there's lots of things you can do. You can self made them with plants with certain sexual reproducing or certain organisms. You can't do this like humans, you can't do it. But with plants you can self made. And that means that the plant pollen can be used to fertilize itself. Self mating is a technique that Mendel used and still a lot of geneticists use today. You can also cross fertilize them, which means that one plants, pollen is used to fertilize another plant. Um Obviously we're talking about plants because we're talking about Mendel's but you can do this with other organisms as well. So when you have your F one generation you can self made it, you can make it with another F. One, you can make it back to its parent, you can make it with anything you want. And generally what will happen is the second filial generation will be produced. Also shorthand F. Two generation. And this is the offspring from the F one mating. So those are the three generations. Now let's go through one of Mendel's crosses as our example. So here we have the parental generation. You can see that he took yellow seeds and green seeded plants and cross them. So here's the parental the offspring of that is called. What Offspring of that parental mating is called? What called the F. one Generation. And what mental saw is that when you made in the yellow seeds with the green seeds you got all yellow seeds in the F. One generation. Then what he did is he took the F. One and he self it meaning that he self fertilized them. So he took the pollen from that F. One plant and used it to fertilize the same F. One plant. When he did this he saw not only yellow but he also saw green in this F. Two generation. So we went from parental F. One and F. Two. So now we're in the F. Two generation. And so he started to count the number of these plants. And to figure out, you know what ratio is it mostly yellow? Is it mostly greed? You know what's going on here? And what he saw is that there were 6022 yellow plants in 2001 plants which equals a total of 8023 total F. Two plants. Now if you do ratio. So if you do six so 22 divided by 8 23 and you do 2001 divided by 8 23. What you'll get approximately is 3/4 and approximately 14. Now it's not perfect. It's never perfect in genetics. It doesn't have to be exactly perfect. But that's approximately what you'll get. And so he noticed that this was a 3-1 ratio and that this ratio kept popping up a lot. Um and this will become very important and we'll talk about this ratio more. But this is just an example of one of Mendel's crosses. So then he took the F. Two generation. So here we're dealing with this one. So we have yellow and we have green. So we took each one of those. So he took a yellow plant and then made the F. Three. So you're getting the pattern here. So we went from parental, we went from F one F. Two and then now we're at F. Three. Now, most of the time in this class, we're gonna stop at F. Two, but just for this example we're gonna keep going throughout three. So in F. Three, he took a yellow F. Two and self did. So he took a yellow F. Two and took that pollen and fertilize that same yellow F. To plant. And what he found is he saw this 3 to 1 ratio again of yellow and green plants. But when he did the same thing with the green F. To plant, he got 100% or four out of four green plants. So that was this is a really important cross to know what Mendel did. So make sure you go back and review and you understand each step of this process. So this is one major cross that he did parental F one all yellow. And he got the F. Two, which was 3/4 yellow and 1/4 green. And then he took each of those F. Two and made it himself them and got different ratios. Then he did a second cross. And what the second cross was was a yellow F. One. This is from the F. One generation and a green. And uh when he made the Yellow F1 with a green, what he saw is that half the offspring were yellow and half the offspring were green. And you're like, okay, well why am I telling you this? It seems like a lot of just like details. Well, the reason that I'm telling you this is because these crosses were crucial to the creation of his laws. So at the end of these crosses, he had no idea. I mean I didn't present to you any alleles or any jeans. I just presented you colors and ratios. And so at the end of these crosses, he knew that yellow seeded plants always produced at least some other yellow seeded plants. He knew that self green plants or green plants used to fertilize themselves, produced only other green seated offspring. And he knew that the green seated plant could skip generations because if we go back up, you can see that here's a generation, the parental generation, here's a second generation, there's no green plants. And then here's the third generation and you can see the green showing back up so we could skip generations. And so he knows nothing about alleles. Right now, we haven't talked about dominance, we haven't talked about recessive, we're just talking about the phenotype, the colors themselves. And so with these three, he was actually able to go ahead and say, you know, these are some of the laws of genetics. And so we're gonna talk about that on the next page. So let's flip the page.

Okay, so now let's talk about Mendel's laws. So Mendel studied pea plants and he was able to make a bunch of observations which led him to conclude certain properties and certain laws about inheritance. So some of these properties that he was able to deduce from these p plant experiments that he did was that there was some type of factor that was important for inheritance. And we call this factor a gene now and this gene is absolutely necessary for producing a certain trait. So for instance, seed color, yellow or green. This gene comes in two forms which we now call eels and we know that these two forms or what they're yellow and green for the example that we used above. So those are the two forms, the alleles come in and then one form or alil is dominant to the other. And that was before when we talked about the example in the previous video, that was the, you know, the yellow produced yellow, green produced green. Um but that the green wasn't always, there is not 100% green, it's actually mostly yellow. And so in this case the yellow would be the dominant. Now we don't know anything about, I haven't told you anything about alleles or homo or hetero I guess or anything like that. We're just going off of colors right now. You know, there's some type of factor that has to be inherited to produce a seed color. This seed comes into color. So there's two forms of this. One hereditary factor or one gene, yellow and green and one form is found more often the other. So it's dominant. Now Mendel's laws, he was able to take those that information and actually make laws that govern genetics is super important. And we're gonna talk, we're gonna mention all three. The last one we're gonna save. It's gonna get its own chapter, which is great. The first two were really going to focus on. So the first one is the law of segregation and this means that ali will separate um and this happens during mitosis. Remember the cell division that creates the sex cells. So alil separate to form gametes. Remember these are sex sells So each gamete contains a single allele for each trade, it either contains yellow or it contains the allele for green or it contains the dominant one or the recessive one, it does not contain both. Gametes only contain one allele. And that is the law of segregation. Then you have a lot of dominance and that states that some alleles are dominant and others are recessive. So in this um in the past ones that we've been talking about with Mendel, it's very clear that yellow is dominant because it's everywhere essentially and green is recessive because the only way you can guarantee if you'll get a green one is a green seated plant is if you self a green seated plant. So if there's no yellow there at all, that's the way you'll get a green, but if there is yellow there, you're gonna get mostly yellow because it's dominant. And then the third law, which I'm not going to talk much about, like I said, it's going to get its own chapter. So we're gonna learn a lot about it. It's a law of independent assortment. And this is a bit more complicated and goes into more detail than what we've discussed so far. But it essentially says genes for different traits segregate into gametes independently. So this is what we're talking about, the color of seeds and the shape of seeds. So it's different. So it's more than one trait. So color and shape, they're gonna separate independently into the sex cells. So it's not that all yellow seeds have to be around. Some of them could be wrinkled or square, or something else. And those genes are going to be divided into gametes, gametes completely independently. Now, if you're a little confused on that, that's okay. Like I said, this law is going to get its own chapter. But what's really important to understand now is this law of segregation, There's one allele per sex cell and the law of dominance, that one of the lille is more dominant. So here's another example. This is a cross of white and red flowers. Now, the notation in this image is a little different than what you would normally see. Um But if we look at this, we can ask, you know, first, we look at the law segregation, which states what that alleles, there's gonna be one allele per gammy. And so where we see this happen, as you can see in the organisms, there's actually two alleles for each organism. But when you see down here, these alleles get separated out. You have one here and one here, one here and one here, and those single alleles are going to be combined together to create the next offspring. And then the second thing you have is the law of dominance, which says that one of these alleles is going to be more dominant than the other. And so if we were just to look at this, if we just look at the presence of white and red flowers here, which one's more dominant? I mean, just taking a guess, knowing nothing about genetics which was more dominant, right? It's very clear the red flower is more dominant because there's so they're all red essentially. Just there's only a couple here that are white. And so it's very clear that the red alil is more dominant. So, those are the first two laws that Mendel proposed. Um So with that, let's now move on.