Meiosis II: Phases

by Georgina Cornwall, PhD

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    00:01 Meiosis II is composed of the same phases. Very familiar operations. Prophase II, metaphase II, anaphase II, telophase II and then certainly cytokinesis. So in prophase II we have two daughter cells resulting from prophase I that now have different genetic content than the parent cell because we have separated homologous chromosomes. Right? So we have reduced chromosome number. Think about this for a moment.

    00:32 We started with 46 chromosomes. We lined them up in pairs down the metaphase plate in metaphase I, and we separated each of those into two new nuclei. So we have 23 in here, and 23 in here.

    00:48 Now, we are going to separate sister chromatids. So, in metaphase we will see that, in metaphase II, we're going to see that the chromosomes align on the metaphase plate. As they align on the metaphase plate, you can see there is some genetic recombination that has occurred. And we see them lining up again single file.

    01:12 So, don't you think that metaphase II of meiosis looks fairly similar to metaphase of mitosis right? Think for a moment. What is the difference here? How is this different than mitosis? We have a reduced chromosome number. So if we were looking at a human cell here, rather than 46 sister chromatids sets lined up down the center, we've already reduced it by half. We had 23 here. 23 here.

    01:45 So we have half the number of chromosomes lined up down the center of the cell. By the way, each sister chromatid is one molecule of DNA. So one long molecule of DNA has been copied into another long molecule of DNA and these are all tightly supercoiled. So in the sister chromatids, we have two molecules of DNA, two molecules of DNA. And those two molecules are about to separate in anaphase. This stuff should be quite familiar by now, right? So as we move forward, in anaphase we see that the sister chromatids are pulled apart. Again, language is critical here. Just as in anaphase of mitosis, anaphase of meiosis II we're separating sister chromatids. Think back. What was the difference during metaphase and anaphase I? What were we pulling apart during anaphase I? We had homologous chromosomes aligned, popped them apart.

    02:55 We were pulling apart replicated homologous chromosomes. So the language again, very important to understanding and being able to answer exam questions on meiosis and mitosis. So telophase, we all know what happens.

    03:11 The nuclear envelope reforms. We now have four distinct cells or four distinct nuclei, and then cytokinesis will follow. We'll have four distinct cells. Now the cool thing is here they are genetically recombined and genetically shuffled. So unlike mitosis, the resulting cells from meiosis are genetically distinct from either of the parent cells. Whether it's sperm being produced or eggs being produced, those are genetically distinct from the parent cells that produced them.

    About the Lecture

    The lecture Meiosis II: Phases by Georgina Cornwall, PhD is from the course Cell Cycle and Cell Division.

    Included Quiz Questions

    1. 14
    2. 7
    3. 28
    4. 56
    1. …four genetically distinct haploid daughter cells from one diploid parent cell.
    2. …four genetically identical haploid daughter cells from one diploid parent cell.
    3. …four genetically identical haploid daughter cells from two diploid parent cell.
    4. …four genetically distinct diploid daughter cells from one diploid parent cell.
    5. …four genetically identical diploid daughter cells from one diploid parent cell.

    Author of lecture Meiosis II: Phases

     Georgina Cornwall, PhD

    Georgina Cornwall, PhD

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