Hi in this video we're gonna be talking about mitosis. So um aosis I feel like a bunch of people get really confused on it understanding what the chromosomes are doing at the certain times and I'm hoping to be able to explain this but my aosis is the process of creating germ cells. These are the sex cells and these cells are used to reproduce. So to germ cells from two different organisms come together called fertilization. And that produces some offspring. Now this one involves so there's two steps. This one involves replicating the D. N. A. And then there are two cells containing a single set of chromosomes. So this is gonna be a Hap Lloyd set. And then my Asus two involves dividing those two cells into four cells with a single set of sister chroma tips. And these are also happy Lloyd. So you start with a deployed cell, you replicate that D. N. A. And you have two steps of mitosis both of which in with hap Lloyd cells. So um here's an example of what what this looks like. So here you start with a deployed cell because you have two copies of every chromosome. You have this blue copy and this red copy. So here's these two sets of chromosomes. You have two copies. So this is deployed, you undergo replication and that gets you this where you have two copies of every chromosome and you can see here the homologous chromosomes that you started with. Um And there's also you can see the colors are switching. There's a process called crossing over that happens here where the genetic information is switched. And we'll talk about that. Um so then you undergo mitosis one. And what happens is you get the two copies of the single homologous chromosomes. So these are half Lloyd and I'll explain why these are Floyd in clear terms in just a minute. And then you have my Asus two which just gets the sister chrome it'd and these are also hap Lloyd. So um biotic DNA duplication and the different divisions that happened results in a lot of different chromosome of forms. And this is where people get really confused. What's the difference between sister chroma tips and homologous chromosomes. And why is it happily, why is it deployed? So let me explain. Sister chroma tides are two copies. So one total pair of each chromosome. So if you start off with this chromosome and you copy it with your replication, these two are sister chroma tides. Now, if you start off with two homologous chromosomes like this, right? And then you replicate each one. Let me start black. These to our sister and these two are non sister and they're both prototypes. Right? These two are homologous chromosomes to begin with. So homologous chromosomes are the two copies of maternal and paternal of both sister chromatic. So here you have homologous chromosomes, Sister chroma tides and non sister chroma tides. Now you have certain terms that all these chromosome forms are called one of them is by violet. And this is when the you may also see this as ted trad actually, Which makes more sense. But essentially it's the same tech trout is when the four sister chromosomes stick together. By violent is when the two homologous chromosomes stick together. Um and so you can see that in my Asus because they're replicated, it ends up being the four sister chromosome. So you can use either term and these separate during mitosis one and um the term half Lloyd means having half the chromosomes of a deployed which has two copies of every chromosome. So let's go through this. So you start with a cell. These are homologous chromosomes. So these are homologous chromosomes. They have the same genes on them. They may have different leal's of those jeans but they have the same genes on them. Now. This is what you start off with. Now replication occurs and you get So here it's deployed, replication occurs and now you have two copies. It's still deployed because you have the same number of chromosomes. You still have a black and blue, you just now have multiple copies of it. So it's deployed these two, both the black, our sister chroma types, both the blue or sister chroma tips. But if you take one black and one blue those are non sister chroma tides. My Asus one happens and this creates a half Lloyd to hap Lloyd selves, one with both copies of the black chromosome and one with both copies of the blue chromosome. And this is why this is half Lloyd because you're still only you only have one chromosome, right? You started with both black and blue, but now you have just black and you can have you have two copies of it and you can have 40 copies of this black chromosome. But it's hap Lloyd because you're down a blue chromosome, you don't have that chromosome anymore. You can have 100 copies of the black but it still hap Lloyd because you only have the black and the same for this, You only have the blue chromosome, you've got two copies of it, you could have 40 billion copies of the blue chromosome, it would still be hap Lloyd because you only have the blue chromosome. Then my Asus two happens and these sister chroma tips get divided. So one gets one of the sister crocheted, so one cell gets one black and the other cell gets the other black and the same for the blue chromosomes here. These are hap Lloyd as well because they either contain the black or the blue. Not both if the cells contain both the black and blue, that's going to be a deployed cell. So this is why my after my Asus one, you have half Lloyd and after my Asus to you also have half Lloyd even though there's different technically chromosome numbers? You look at the type of chromosome is it black or blue and how many of those you have? So with that? Let's not move on.
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Okay, so we know that mitosis involves a lot of genetic variation. So um this is because D. N. A. Is reorganized and shuffled around to produce genetically distinct offspring. So I'm going to talk about a few of the terms and the fruit of the processes that happens during mitosis to get this genetic shuffling. So one of them is called homologous recombination. So homologous recombination allows for chromosomes to exchange similar DNA sequences. So we've talked about this before in DNA repair and but this is a little different um aosis. So in DNA repair we talked about using identical DNA sequences to repair the D. N. A. But homologous recombination in mitosis actually uses non identical but similar sequences from non sister chroma tides in the by violent. So what do I mean by by violent? Remember by violence is going to be the four sister chroma tides 1234. So the identical. So if I was wondering wanted to do recombination for chromosome or for a sister chromatic one, um the identical sequence would be from to the identical. But if I wanted a non identical but similar, I could choose either from four or from three. And so that's how so DNA repair would always use two. Whereas mitosis is going to use the non identical sequence from three or four. So that's homologous recombination that shuffling between similar DNA sequences, then the second form is through crossing over. So crossing over is when maternal and fraternal homa logs physically swaps chromosomal segments. So what we get here is we have a maternal and we have a paternal chromosome and if there's a segment right here, they'll that it can come over here and that one will replace and they'll swap the segments. So what this is called is when these are connected they're called cosmo or cosmo to um and this is hold by violence together because um aosis we're dealing with a lot of genetic information. So that would be these are the by violence. So the cosmo to would form like here and here that would connect the by violence together. We're crossing over has occurred. And this is super important because it actually keeps the by violence together and keeps them from separating early during mitosis. And we'll talk about that more in just a minute. And then finally we have reassortment and this is just the random division of chromosomes into cells. So remember during meta phase, the chromosomes line up in the middle and then they separate from each other during an A phase. But which side they actually are lining up is kind of random. So which chromosomes the cell gets is entirely random. So that's called reassortment. Now this doesn't necessarily have to be successful. And so non disjunction actually describes when the Houma logs fail to separate. So remember we have these chromosomes that line up in my Asus and so the order. So this is 12 and this is three and four. So the order in which these line up and which ones get separated out to the two cells completely random. And so if non disjunction occurs and say both of these chromosomes go here. This one goes here and this one goes here. What we get is we get one pair of chromosomes here and three here. So that's non dysfunction. And so this causes what we say is an employee and that's where there are eggs. Um Typically eggs which are the sex cells with the wrong number of chromosomes. So we see this in Down syndrome, also called trisomy because there are eggs, there's an extra chromosome there. So this is what it looks like during crossing over. You can see these maternal and what that damn maternal and paternal chromosomes. They eventually cross over the points where they cross over. It's called the cosmo. To and then after the end, you can see that now they have mixing of genetic information. So that is a bunch of different ways that genetic shuffling happens during mitosis. So with that let's not move on.
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Okay, so now we're going to go through the mitosis step. So mitosis one occurs first and the steps are the exact same as mitosis. They're just given either a one or a two because it happens, there's mitosis one and there's mitosis too. So the first step is going to be pro phase one. Um and there's actually some extra distinctions here that you need to know about. Um So there's actually five phases of pro phase. And you're gonna ask, do I actually need to know these and you are gonna have to know these um these five different phases. But the important one, I think probably one of the most important one is this one here because this is where crossing over occurs. But you can see there's lots of different things that are happening during pro bass. You have condensation of chromosome fibers, you have more condensation, the by violence form. Then you have crossing over, which is going to be a super important one to know. You then have this phase where they're still attached together and then you have nuclear envelope breakdown where the spindle forms. So this is another probably really important one to know. Um So if I were to pick the top two of these five steps to know this is the one and this is the one to really know. So this is what it looks like. Let me back up while I talk about this. So here we have the cell that we started with, we obviously have some type of DNA replication because we have two of these um red and two of these green chromosomes here. And you can see crossing over Has begin to occur and pro Phase one because the green and the red are mixing. So then we get meta Phase one. So these by violence are gonna align at the spindle equator. So what this means, it just aligns in the middle. So here's the cell you can see the by violence are aligned. So you have your one, you have your four sister chroma types 234. You have your two homologous chromosomes that have lined now in the middle. And notice here that the that the way that these are lined up is different than the way that they're lined up in um mitosis. Notice that you have the four sister chroma tips lined up here, right next to each other. So the by violence lined up in the middle. And the cais mata which remember formed during crossing over is what allows for these four sister chrome attempts to align at the middle. So without the cosmo to they would actually break apart. And then you would get all sorts of horrible like genetic information being split improperly. But instead because there's crossing over the cosmo to keeps these by violence or the four sister chromosomes together that they can line up now in the middle. Then you get an A phase one to the home august homologous chromosomes separate. So notice here these are the ho mal agus chromosomes they're separating. So you're getting a full set of chromosome here in full set of chromosome here. So each chromosome has to to sister chroma teds and then you finally get tell a phase one inside of genesis. And that this produces the two cells. These cells contain a single randomly sorted chromosomes. So you get the two sister chromosomes that you know it just r random whichever side it divides on. And then um the confusing part about this is because some people call this deployed, which I think it's deployed right? Because I mean you're clearly have um I mean I think this is I mean clearly have the genetic information. You should this is clearly deployed to me. But some of them and some of you might see this as hap Lloyd. I think this is super confusing because it's just referring to a half Lloyd set of chromosomes but I think that this is a horrible way to describe it. But you may see it as half Lloyd. This is I think it's easier to just say, you know, this is deployed. So then we in turn to may assist to which is the pro phase is much more simpler. It's really short. It's pretty much almost non existence. There's no DNA replication here. Only pro phase one has DNA replication. Pro phase two does not. Um And then you immediately after that you go into meta phase two where the chromosomes again line up at the equator. But notice here that when they're lining up. So here's pro fes there's really nothing going along here and then we have meta phase. But notice here, whereas before we had four sister chromosomes lining up in the middle. Now we have to. So I think that's a good way to kind of realize, you know, am I met a phase one or phase two? Just count the number of sister chroma tides that have lined up in the middle. So here we have 12 sister chromatic. So we now know we're on to phase two. Once this lines up, we then undergo and a phase two where the sister chroma tides are now separated. And finally we get to tell a phase two inside a kinesis where two more cells are produced. Each cell contains a set of sister chroma tides and these are referred to as hap Lloyd. So what we get here is the sister chroma tides are now separated and each of these cells gets one of the set of sister commented. So now we have to sister competence here. So that is my aosis in a nutshell. Um so with that let's not turn the page
Meiosis and Animal Life Stages
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Okay, so now let's talk about mitosis and animal life stages. So like I said before not all animals use mitosis to create sex cells. So let's go over some of the organisms that don't do that. So anIM files are classified into three groups depending on where in their life cycle they form aosis. So the first group is called comedic or terminal mitosis. So these are the organisms that we're most familiar with. They used my aosis to produce gametes or sex sells. So this is going to be us, including humans, most living organism. And then they say that may assist. This type of mitosis is complete after fertilization because you get to have Floyd cells coming together, agora sperm forming a deployed cell. So this is the one we are most familiar with. Now the other two were not as familiar with. So the second one is psychotic or initial mitosis and these are organisms that use my Asus after fertilization. So mitosis is used to perform to create spores that are hap Lloyd. And so the actually the unique thing about this is it's kind of different. So deployed cells are actually the gametes and half Floyd cells are the normal organism. So that is the unusual part of that. So these produce hap Lloyd spores and the deployed supporters of the gametes and then finally we have the third one which is sport or intermediate mitosis and then this in this case my Asus actually has nothing to do with gamete formation or fertilization at all in any way. So what you get is you get sparrow fights. These are deployed cells that undergo mitosis. Then you have spore a genesis and so mitosis produces these cells called Amido fights. And then Gambino fights are produce gametes through mitosis. So you get spore A genesis um where my aosis forms fights. And then gamer fights produce gametes through mitosis, mitosis has nothing to do with the production of gametes which occurs through mitosis. So here's an example of sporks intermediate uh manoa sis. So you see here you have this poor fight. It undergoes mitosis which produces these spores. The spores then undergo mitosis to produce the camino fight. The camino fight then produces gametes through more mitosis. The gametes come together fuse form a zygote, there's more mitosis. Then the spore fight can produce spores via mitosis. So you can see that the gametes are all the way over here and mitosis is all the way over here. So they really have nothing to do with each other. And that's kind of the example of the spork intermediate mitosis. So there's some probably some unique ways that my Asus has handled in different organisms. So with that let's now move on
In which of the following phases does crossing over occur?
In which of the following steps of prophase I does crossing over occur?
The cells produced from meiosis I and meiosis II are both haploid?
Fill in the blanks. In anaphase I the _____________ separate, while in anaphase II the ____________ separate.
Sister chromatids, homologous chromosomes
Homologous chromosomes, sister chromatids
Homologous chromosomes, Homologous chromosomes
sister chromatids, sister chromatids
Which of the following life cycles uses meiosis after fertilization?