How do the resulting cells at the end of meiosis compare to the original cell from the beginning of meiosis?

Mitosis and meiosis, which are both forms of division of the nucleus in eukaryotic cells, share some similarities, but also exhibit distinct differences that lead to their very different outcomes. Mitosis is a single nuclear division that results in two nuclei, usually partitioned into two new cells. The nuclei resulting from a mitotic division are genetically identical to the original. They have the same number of sets of chromosomes: one in the case of haploid cells, and two in the case of diploid cells. On the other hand, meiosis is two nuclear divisions that result in four nuclei, usually partitioned into four new cells. The nuclei resulting from meiosis are never genetically identical, and they contain one chromosome set only—this is half the number of the original cell, which was diploid.

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• Video transcript
• How do cells at the completion of meiosis compare with the cell from which they were derived?
• How do the cells at the end of mitosis compare to the original cell?
• How do the products meiosis compare to the original cell?
• How does the end result of meiosis differ from the end of mitosis?

The differences in the outcomes of meiosis and mitosis occur because of differences in the behavior of the chromosomes during each process. Most of these differences in the processes occur in meiosis I, which is a very different nuclear division than mitosis. In meiosis I, the homologous chromosome pairs become associated with each other, are bound together, experience chiasmata and crossover between sister chromatids, and line up along the metaphase plate in tetrads with spindle fibers from opposite spindle poles attached to each kinetochore of a homolog in a tetrad. All of these events occur only in meiosis I, never in mitosis.

Homologous chromosomes move to opposite poles during meiosis I so the number of sets of chromosomes in each nucleus-to-be is reduced from two to one. For this reason, meiosis I is referred to as a reduction division. There is no such reduction in ploidy level in mitosis.

Meiosis II is much more analogous to a mitotic division. In this case, duplicated chromosomes (only one set of them) line up at the center of the cell with divided kinetochores attached to spindle fibers from opposite poles. During anaphase II, as in mitotic anaphase, the kinetochores divide and one sister chromatid is pulled to one pole and the other sister chromatid is pulled to the other pole. If it were not for the fact that there had been crossovers, the two products of each meiosis II division would be identical as in mitosis; instead, they are different because there has always been at least one crossover per chromosome. Meiosis II is not a reduction division because, although there are fewer copies of the genome in the resulting cells, there is still one set of chromosomes, as there was at the end of meiosis I.

Cells produced by mitosis will function in different parts of the body as a part of growth or replacing dead or damaged cells. They may even be involved in asexual reproduction in some organisms. Cells produced by meiosis in a diploid-dominant organism such as an animal will only participate in sexual reproduction.

Figure 1 Meiosis and mitosis are both preceded by one round of DNA replication; however, meiosis includes two nuclear divisions. The four daughter cells resulting from meiosis are haploid and genetically distinct. The daughter cells resulting from mitosis are diploid and identical to the parent cell.

References

Unless otherwise noted, images on this page are licensed under CC-BY 4.0 by OpenStax.

OpenStax, Biology. OpenStax CNX. May 27, 2016http://cnx.org/contents/:1Q8z96mT@4/Meiosis

Video transcript

- [Voiceover] Before we go in-depth on meiosis, I want to do a very high level overview comparing mitosis to meiosis. So, in mitosis, this is all a review, if you've watched the mitosis video, in mitosis, we start with a cell, that has a diploid number of chromosomes. I'll just write 2n to show it has a diploid number. For human beings, this would be 46 chromosomes. 46 for humans, you get 23 chromosomes from your mother, 23 chromosomes from your father or you can say you have 23 homologous pairs, which leads to 46 chromosomes. Now after the process of mitosis happens and you have your cytokinesis and all the rest, you end up with two cells that each have the same genetic information as the original. So you now have two cells that each have the diploid number of chromosomes. So, 2n and 2n. And now each of these cells are just like this cell was, it can go through interphase again. It grows and it can replicate its DNA and centrosomes and grow some more then each of these can go through mitosis again. And this is actually how most of the cells in your body grow. This is how you turn from a single cell organism into you, or for the most part, into you. So that is mitosis. It's a cycle. After each of these things go through mitosis, they can then go through the entire cell cycle again. Let me write this a little bit neater. Mitosis, that s was a little bit hard to read. Now what happens in meiosis? What happens in meiosis? I'll do that over here. In meiosis, something slightly different happens and it happens in two phases. You will start with a cell that has a diploid number of chromosomes. So you will start with a cell that has a diploid number of chromosomes. And in it's interphase, it also replicates its DNA. And then it goes through something called Meiosis One. And in Meiosis One, what you end up with is two cells that now have haploid number of chromosomes. So you end up with two cells, You now have two cells that each have a haploid number of chromosomes. So you have n and you have n. So if we're talking about human beings, you have 46 chromosomes here, and now you have 23 chromosomes in this nucleus. And now you have 23 in this nucleus. But you're still not done. Then each of these will go through a phase, which I'll talk about in a second, which is very similar to mitosis, which will duplicate this entire cell into two. So actually, let me do it like this. So now, this one, you're going to have four cells that each have the haploid number that each have the haploid number of chromosomes. And they don't all necessarily have the same genetic informatioin anymore. Because as we go through this first phase, right over here of meiosis, and this first phase here you go from diploid to haploid, right over here, this is called Meiosis One. Meiosis One, you're essentially splitting the homologous pairs and so this one might get some of the ones that you originally got from your father, and some that you originally got from your mother, some that you originally got from your father, some that you originally got from your mother, they split randomly, but each homogolous pair gets split up. And then in this phase, Meiosis Two, so this phase right over here is called Meiosis Two, it's very similar to mitosis, except your now dealing with cells that start off with the haploid number. It's important to realize that meiosis is not a cycle. These cells that you have over here, these are gametes. This are sex cells. These are gametes. This can now be used in fertilization. If we're talking about, if you're male, this is happening in your testes, and these are going to be sperm cells If you are female, this is happening in your ovaries and these are going to be egg cells. If you a tree, this could be pollen or it could be an ovul. But these are used for fertilization. These will fuse together in sexual reproduction to get to a fertilized egg, which then can undergo mitosis to create an entirely new organism. So not a cycle here, although these will find sex cells from another organism and fuse with them and those can turn into another organism. And I guess the whole circle of life starts again. But it's not the case with mitosis where this can keep going and going, going. This cell is just like this cell, while these sex cells are differeent than this one right over here. Now, where does this happen in the body? We've talked about this in previous videos. These are your somatic cells right over here. These are the ones that make up the bulk of your body, somatic cells. And where is this happening? Well, this is happening in germ cells, As we mentioned, if you're male it's in your tesis and if you're female it's in your ovaries. And germ cells actually can undergo mitosis to produce other germ cells that have a diploid number of chromosomes, or they can undergo meiosis in order to produce sperm or egg cells in order to produce gametes.

How do cells at the completion of meiosis compare with the cell from which they were derived?

How do the cells at the end of mitosis compare to the original cell?

How do the products meiosis compare to the original cell?

How does the end result of meiosis differ from the end of mitosis?