Mitosis vs Meiosis

okay so this is my updated version of my eternal battle of good versus evil and the process of mitosis versus meiosis you know every year I teach this lesson and students will sometimes mix up a few stages so I hope this video will help clarify so what the picture shows is a cell going through the process of mitosis a human cell has 46 chromosomes that is what we call the diploid chromosome number and in the process of mitosis a diploid cell with 46 chromosomes will divide into two cells each of them also containing 46 chromosomes well that's a little different when we compare and contrast with meiosis in the picture we see a cell starts very similar when it goes to the process of meiosis a cell a human cell will start with 46 chromosomes but through the process of meiosis that 46 chromosome cell will divide not once but twice into a total of four cells in each of the four cells has half the total number of chromosomes that's what we call the term haploid haploid cells have half the total number of chromosomes and in humans half of 46 is 23. so how does this process take place how how do what are the stages of similarities and differences between mitosis and meiosis that's what this video is all about let's go ahead and get started so here we have two cells and the cell on the top will eventually go through mitosis and the cell on the bottom will eventually go through meiosis right now both of these cells are an interphase interphase takes place prior to mitosis and interphase takes place prior to meiosis and what I want to do is first count out the amount of Chromatin DNA strands of DNA that are in the nucleus of these two cells and so I want to make a note you know just to start in the top cell we're starting with a cell that has four strands of DNA one look at the bottom cell in the bottom cell we also see a cell that has four strands of DNA and just so we don't forget that number I'm going to go ahead and make a note of it in the lower left hand corner and that note is going to stay there the whole time as our silent reminder of how much DNA was in each of these two cells at the start so they each have four strands of DNA called chromatin well now that we're going to go through this process what happens during the S stage of interphase you can see the DNA the DNA just duplicated the chromatin strands duplicated and that happens in the S stage of interphase which is prior to mitosis now in the cell to the bottom the same thing the cell to the bottom is going to duplicate the strands of DNA it's going to duplicate the chromatin that happens during the S stage of interphase which is prior to meiosis so so far the two cells are setting up to be fairly fairly similar to one another well let's move on now we're going to move on to the step known as prophase and let's look at the cell on top it's going to go through the prophase stage of mitosis and so what happens is the nucleus is going to dissolve and you see the blue circle disappearing the next thing that I want to note is look at the bottom cell the bottom cell is also going to lose its nucleus as it goes through prophase number one of meiosis in the top cell what I want to draw your what I want to draw your attention to in the top cell now is that the chromatin the strands of Chromatin that were just duplicated are going to coil into chromosomes I'll explain the p and the m in just a moment in the bottom cell prophase number one of meiosis really the same thing is going to happen the chromatin is going to coil into chromosomes now I want to mention what the p and what the m stand for the p and this key is going to stay up here for a little bit the P stands for chromosomes that are paternal paternal chromosomes are chromosomes you inherited from your father the m stands for maternal these are chromosomes you inherited from your mother so notice how we have a chromosome number one maternal and a chromosome number one paternal M1 and P1 we in both cells there's also a P1 which means excuse me in both cells there's also a M2 which means chromosome number two from the mother and there's also a P2 which means chromosome number two from the father so m means maternal from the mother p means paternal from the father well let's move on with the process so now that the chromosomes have formed let's focus our attention on the bottom cell prophase number one of meiosis something else is going to happen there's a process called synapsis that's about to happen in the animation this only happens in prophase number one of meiosis watch what happens during the process called synapsis the two homologous chromosomes are paired up with one another the two chromosome number ones are paired up with one another the maternal chromosome number one and the paternal chromosome number one the same thing happens with chromosome number two the maternal and the paternal chromosome number twos are paired up with one another this pairing up of homologous chromosomes is called synapsis this only happens during prophase number one of meiosis and when synapsis is finished uh this is what's created these groupings of chromosomes here are called a tetrad Tetra is a prefix that means four and the reason it's called a tetrad is because you see the bracket in the picture is around two chromosomes but remember that one chromosome is made from two chromatids so if there's two chromosomes in a tetrad that's a total of four chromatids that's how they get their name this process called synapsis only occurs in prophase number one of meiosis okay so the next thing I want to mention now that synapsis has occurred the next thing I want to mention is a process known as crossing over and this only happens in prophase number one of meiosis watch this in crossing over parts of the chromosomes are going to swap with one another watch the animation three two one parts of the chromosome swapped with one another parts of the maternal and the paternal chromosomes swapped with one another if you missed it here it is again on the other on the other tetrad so in crossing over parts of the maternal chromosome number one break away and connect with the paternal chromosome number one so the maternal and the paternal break off parts of their chromosomes and they recombine with one another this process called crossing over shuffles up the genetic Gene combination just a little bit and we'll see why that's relevant near the end so now when we go on to the next stage called metaphase on the top let's look at metaphase of mitosis in metaphase of mitosis the four chromosomes in the animation are randomly pulled to the middle of the cell look at the bottom animation now in metaphase number one of meiosis those two tetrads are going to be pulled randomly to the middle of the cell and that's really all that takes place remember who's pulling the chromosomes here are those spindle fibers and so let's move on to anaphase so now the top again anaphase of mitosis what happens next here it is what happens next is the chromatids the sister chromatids are pulled apart from one another the spindle fibers will pull one of the chromatids to the left the other chromatid to the right so the chromosome is ripped apart one chromatid pulled to the left one chromatid pulled to the right well now what about the meiosis stage anaphase number one of meiosis watch this the chromosomes are pulled apart so the chromosomes are still into I should say the tetrads were pulled apart and the but the chromosomes are still intact two entire complete chromosomes were pulled to the right two entire complete chromosomes were pulled to the left so that's a bit of a distinction that's different between the mitosis on top and the meiosis and the bottom let's move on into telophase so in the telophase part of this pres of this project this presentation the process known as cytokinesis is going to start to split the side of the cytoplasm of the cell and the two cells are going to split in half you know sometimes cytokinesis starts during anaphase but I just threw it in here in the telophase because this is kind of the final step telophase is the final step of mitosis so cytokinesis is going to split the one cell into two when the cytoplasm divides the next thing that's going to happen is around those four bits of DNA that you see is the nucleus is going to regrow the nucleus offers protection for the DNA that's inside and finally the chromatids those four chromatids are going to unwind back into the linear strands of Chromatin very similar to how we started this this video and that's really it that's really the end result but look at the bottom one we're going to see the bottom one's not finished first of all in the telophase number one of meiosis you just saw cytokinesis split the two cells in half well what happens next the nucleus regrows and sometimes the nucleus does not regrow but in this animation we're going to show you what happens when the nucleus does regrow the nucleus regrows and that's really it the the chromosomes are not going to unwind into chroma tin so that's really it telophase number one of meiosis but we're not quite done because this was just telophase number one there's a round two of all this in just a moment for meiosis so when we look at the top cell the top cell's finished mitosis is over we started with two uh excuse me we started with one cell with four strands of DNA and we ended with two cells with four strands of DNA but now let's look at the bottom we can focus on the bottom now prophase number two of meiosis there is no interphase number two just moves right on into prophase number two and like it says the nucleus is going to often redissolve and so there it goes and when we continue on when we continue on to metaphase number two of meiosis the chromosomes are going to be pulled to the middle of the cell remember who's pulling the chromosomes that would be the spindle fibers so the chromosomes are pulled to the middle of the cell when we move on into anaphase number two of meiosis now the chromatids are going to be pulled apart so the chromatids get pulled to opposite ends of the cell and this animation the chromatids one of the chromatids went to the top the other chromatid went to the bottom so the chromosomes that were lined up in the middle during metaphase the chromosomes were ripped apart with one chromatid going each Direction and when we finally move into telophase number two of meiosis well the cytoplasm is going to split again during the process called cytokinesis so the two cells have just split into four the nucleus is going to regrow but now it's going to regrow in four cells and the last thing that's going to happen here is the chromatids are going to unwind back into their linear version linear strands of DNA called chromatin and that's really the end of meiosis number two here so when you look at the end result what we finished with is four haploid cells so just to wrap up this and kind of give this quick conclusion here if you notice I want to point your attention to the box in the upper left hand corner when we started this video there were four strands of DNA in the one cell at the top well let's count up the strands of DNA now the new cells the two new cells on top look at that four strands of DNA in the cell on the left and four strands of DNA in the cell on the right so the cell started with four strands of DNA and the two that are created each have four strands of DNA as well and not only that but both cells are identical they each have two fully black strands of Chromatin they each have two fully red strands of Chromatin the cells are identical to one another well now let's focus our attention to the one on the bottom so the cells on the bottom just went through meiosis but remember at the start they each had four strands of DNA in them let's count up the strands of DNA now the new cells have half the amount of Chromatin as they did from the start look at that that cell only has two the cell in the upper right hand corner only has two strands of Chromatin the cell in the lower left only has two strands of Chromatin the cell in the lower right only has two strands of Chromatin so the Cell at the beginning had four strands of DNA but these cells only have two well that's because these are haploid cells created by meiosis another thing I want to point out is that each cell is genetically unique picture of red and black strands of Chromatin because the process called crossing over which took place way back in prophase number one so that is one of the unique the major unique differences of meiosis which does not happen during mitosis and this really will conclude this video right here so the cells on top the cells on top started to go through my went through mitosis and so cells that go through mitosis will start diploid and n-diploid but the cells on the bottom cells that will go through meiosis will start diploid but at the end they're going to have half the amount of Chromatin and they're going to end haploid so that's it that's the updated video I hope you like it better than the original one I tried to be a little more thorough by adding crossing over so I hope you I hope this was helpful and good luck in your understanding of mitosis versus meiosis

Channel: Beverly Biology

Views: 1,268,969

Keywords: Meiosis, Mitosis, Stem Cell (Field Of Study), Biology (Media Genre), Science (Journal)

Id: bRcjB11hDCU

Length: 15min 25sec (925 seconds)

Published: Sun May 04 2014