Meiosis?? Can anybody help me understand what they are??
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>meiosis (mīŏ'sĭs) , process of nuclear division in a living cell by which the number of chromosomes is reduced to half the original number. Meiosis occurs only in the process of gametogenesis, i.e., when the gametes, or sex cells (ovum and sperm), are being formed. Because fertilization consists of the fusion of two separate nuclei, one from each of the sex cells, meiosis is necessary to prevent the doubling of the chromosome number in each successive generation. An ordinary body cell is diploid; i.e., it contains two of each type of chromosome. The members of each pair are known as homologous chromosomes. An ovum or sperm is haploid; i.e., it contains only a single chromosome of each type and, therefore, half the number of chromosomes of the diploid cell. When the two haploid cells fuse, the diploid number is restored, and the plant or animal growing from the fertilized egg (zygote) has the usual diploid number of chromosomes in its cells. Just before meiosis each chromosome replicates to form two identical copies in the form of strands called chromatids joined together at a point called the centromere. In the first stage of meiosis, called the reduction division, the members of each pair of homologous chromosomes lie side by side and crossing over occurs. Each member of the pair then moves away from the other toward opposite ends of the dividing cell, and two nuclei, each with the haploid number of double-stringed chromosomes, are formed. Thus at the beginning of the second meiotic sequence, called the equational division, each cell nucleus contains one chromosome from each homologous pair and each chromosome is of two strands that are identical (except where crossing over has occurred). Then the chromosomes separate into their single strands which move toward opposite ends of the dividing nucleus. The result of meiotic division is four cells, each haploid, with one chromosome of each pair.\n\n>meiosis (meye-oh-sis) \nDivision of cells in which four “daughter” cells are produced from one “parent” cell, each with half the genes of the parent. Meiosis is a key process in sexual reproduction. In the ovaries and testes, meiosis produces a great variety of sex cells (sperm and ova), because the genes of the parent cell can be split in many different ways. The sex cells combine in fertilization to produce a new individual with the full number of genes — half from each parent. Because the sex cells come in such variety, and come from two parents, there is an enormous number of possible forms for the offspring. (See chromosomes, genetics, and mitosis.) \n\n>mei·o·sis (mī-ō'sĭs)\nn., pl. -ses (-sēz').\nThe special process of cell division in sexually reproducing organisms that results in the formation of gametes, consisting of two nuclear divisions in rapid succession that in turn result in the formation of four gametocytes, each containing half the number of chromosomes that is found in somatic cells.\n\n>meiosis: \nIn biology, meiosis is the process that transforms one diploid cell into four haploid cells in eukaryotes in order to redistribute the diploid's cell's genome.\n\nMeiosis forms the basis of sexual reproduction and can only occur in eukaryotes. In meiosis, the diploid cell's genome, which is composed of ordered structures of coiled DNA called chromosomes, is replicated once and separated twice, producing four sets of haploid cells each containing half of the original cell's chromosomes. These resultant haploid cells will fertilize with other haploid cells of the opposite gender to form a diploid cell again. The cyclical process of separation by meiosis and genetic recombination through fertilization is called the life cycle. The result is that the offspring produced during germination after meiosis will have a slightly different blueprint which has instructions for the cells to work, contained in the DNA. This allows sexual reproduction to occur.\n\nBiochemically
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Meiosis is also known as reduction division.\nIt is a type of nuclear division that gives rise to four reproductive cells (gametes) each with half the chromosome number of the parent cell. Two consecutive divisions occur. In the first, homologous chromosomes become paired and may exchange genetic material before moving away from each other into separate daughter nuclei. This is the actual reduction division because each of the two nuclei formed contains only half of the original chromosomes. The daughter nuclei then divide by mitosis and four haploid cells are produced. Four stages, prophase, metaphase, anaphase and telophase\n\nMitosis is a type of nuclear division that results in two daughter cells each having a nucleus containing the same number and kind of chromosomes as the mother cell. each chromosome divides lengthwise into two chromatids, which seperate and form the chromosomes of the resulting daughter nuclei. Four stages as well prophase, metaphase, anaphase and telophase, which merge into each other. Mitotic divisions ensure that all cells of an individual are genetically identical to each other and to the original gertilized egg.
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Mitosis and Meiosis are the two types of cell divison. \nMitosis:\nhttp://www.cellsalive.com/mitosis.htm\nMeiosis:\nhttp://www.cellsalive.com/meiosis.htm
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I think one is the division of chromosomes and that is just a guess as for the other I assume that it has something to do with two sexes becoming one.
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I scanned a diagram I have into the computer, I hope this helps:\n\nhttp://i74.photobucket.com/albums/i267/Miles_Tails_Prower__/Aminals007.jpg\n\nBy the way Crimedog, you are thinking of Mitosis.  Meiosis is for sexual reproduction while mitosis is the asexual reproduction of eukaryotic cells.  (yoo-ku-rO-tic - cells with membrane-bound organells)
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Meiosis, on the other hand, is only used for making gametes!   Why do we need a special type of cell division just for making gametes?  There are two ways to answer this question.  The first is that when we produce our next generation, we do not wish to make identical individuals to ourselves... instead, we make unique individuals, different from either parent.  In order to do that, we have to be able to mix up our own genetic information into new combinations; it is these new combinations that come together during fertilization, producing an entirely unique, new individual.  Mitosis does not allow for any mixing up of genetic information-- instead, it preserves genetic information perfectly to make identical daughter cells.   Meiosis does the opposite-- meiosis jumbles up our genetic information into new combinations.\n\n    The second reason that we have to use meiosis is because we need our spermatozoa and ova to contain only half of the normal amount of genetic information.  Keep in mind that during fertilization, the spermatozoan and ovum fuse together into one, combined cell (called the zygote).  That means that their genetic information also comes together.  When each gamete has half of the normal amount of genetic information, they can come together and make a whole.  From that point forward the embryo (and then fetus and then neonate...) has a new set of genetic information, half from each parent, that is preserved for all the cells of its forming body.
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Hi Erica, \n\nI'd waste both your and my time if I try to answer this question with lots of detail. I'd suggest you go to your textbook, flip a few pages here and there, get a broad idea and then, come back and read this answer. \n\nPlease notice that I'll have to make this answer less complex by generalizing concepts and avoiding some fine details which you can easily read in your textbook.\n\nNow, without wasting much time, here is my answer-\n\n===================\n\nCharacteristics of animal sexual life cycles-\n\n1- Usually, there are two parents- male and female. Both form special haploid cells called gametes by meiosis.\n\n2- Gametes fuse in pairs to form diploid cells called zygotes (fertilization).\n\n3- Repeated mitotic divisions of the zygote forms embryos.\n\n4- And the embryo develops into a new individual.\n\nSooo simple!\n\n====================\n\nCharacteristics of plant sexual life cycles-\n\nIt is same as animal sexual reproduction. Just that the technical terms and the methods of reproduction are a little different in flowering and non-flowering plants. I suggest you to read your textbook for the detailed terminology.\n\nIn plants-\n\n1- Diploid sporophytic cells divide by meiosis to give haploid gametophytic cells.\n\n2- Haploid gametophytic cells from male and female fuse to form the diploid zygote.\n\n3- The zygote then develops into an embryo and then to a full diploid plant body.\n\n* There are lots of finer details like the flowering system in flowering plants: pollens, ovules etc. and sporangia in non-flowering plants. I suggest you to study the life cycles of different bryophytes, gymnospermae and angiospermae to get the idea.\n\n================\n\nCharacteristics of fungal sexual life cycles-\n\n1- It involves fusion of two compatible sex cells/ gametes. The sex organs that produce gametes are called gametangia.\n\n2- The gametangia of fungi are unicellular and are surrounded by a sterile jacket. In fungi, there is a gradual reduction in sexuality from lower to the higher fungi.\n\n3- In the first stage, the cytoplasms of two sex cells fuse with each other but the nuclei do not fuse. The cell is thus called a dikaryon. (Plasmogamy).\n\n4- The nuclei then fuse to form the synkaryon. (Karyogamy).\n\n5- The diploid cell after that, produces haploid nuclei by meiosis.\n\nThere are broadly five types of sexual fusion in fungi.\n\nHere they are-\n1- Planogametic copulation. \nOne or both of the gametes are motile.\n\n2- Gametangial contact. \nThe two gametangia come together and the male gametangia forms a tube through which the male non-motile gamete is sent to the female gametangia.\n\n3- Gametangial copulation. \nThe gametangia themselves fuse together and lose their sexual identities to form zygospore.\n\n4- Spermatization. \nNumerous spore-like minute bodies (spermatia) are sent through various agencies to the receptive hyphae or trychogyne of female gametangium.\n\n5- Somatogamy.\nIn this mode, sex organs are not formed and the fusion occurs two vegetative cells resulting in the formation of dikaryon.\n\n=================\nI hope the above info helps.
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Check out "mitosis" in a suitable source (Wikipedia, for example).  The process is a bit long to describe here.
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1.synapsis occur only in meiosis. \n2.mitosis divide once, where meiosis divide twice. \n3.mitosis produce two daughter cells that are genetically identical to the parent cell, where meiosis produce four daughter cells that have only half of the chromosomes the mater cell had. \n4.meiosis have their homologous chromosomes separate!! but mitosis don't.
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During meiosis, sexually reproducing organisms choose one of the two versions of each chromosome they have (the two versions are supplied because each parent provides one copy of each chromosome) to be included in the haploid gametes. Because one copy of two possible choices has to be made for each of the 4 chromosomes (diploid number of 8 is referring to the fact there are 2 copies of each of 4 chromosomes meaning 8 total). \n\nTo figure out the number of possible combination you use a simple probability formula. \n\nThere are 2 choices for the first chromosome location x 2 possible choices for the second location x 2 possibilities for the third location x 2 possibilities for the final location\n\n2x2x2x2 = 16 possible combinations that can be made in any one gamete.\n\nOf course this is the absence of any crossing over event, which can produce an incalculable number of possible rearrangements.
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Penguin says >>\n\nOogenesis is the process of females creating egg cells... When women are born, they have a lot of cells that of those egg cells, only a few will undergo meiosis and form egg cells. Meiosis, yes, does form four haploid cells from each one of those "pre-made egg cells". All those four haploid cells has 23 chromosomes. However, Meiosis only ensures that there are enough chromosomes for the offspring, and not necessarily the quality of the egg cell... \n\nWhat I mean is >> The larger egg cell containing more cytoplasm lives, while the other doesn't develope into an ovum. \n\nIn Meiosis I, the original cell divides into two, with 46 chromosomes. Meiosis does not seperate into two equal cells, as they do in mitosis. The larger cell then splits again [Meiosis II], and of the two haploid cells that result from Meiosis II, the larger one lives again. So, only one gamete is formed, though of the 4 haploids, 3 of the haploids degenerate. \n\n-- Cytokinesis isn't part of mitosis...Mitosis is part of the cell cycle, which has 3 steps :: interphase, mitosis, and cytokinesis. \n\nRemember that mitosis is the process of splitting a cell's nucleus. \n\nand remember that cytokinesis only splits two cells in half by pinching the cell membrane...\n\nSo... there's a difference. \n\nThank -you-\n\n<< Penguin waves good bye.
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two cell divisions.... one for meiosis 1 and one for meiosis 2
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Well, as you may already know, the purpose of both mitosis and meiosis is to take one cell and make two cells. Before the cells do this though, they have to make sure that a few things are in order. Obviously, there has to be enough stuff for the 2 cells to each be able to live independently. so, there has to be duplication of a lot of stuff before the first cell (let's call it the parent) divides. One of these things is the genome. These are the chromosomes which are made up of DNA. Once the DNA replicates (makes 2 copies of everything from what the parent originally had), the cell can divide. There are now 4 chromosomes of each type, we started out with our usual 2 of each (most organisms have 2 of each chromosome and they differ slightly from each other-this becomes important for meiosis), then when everything duplicated, we got 4! \n\nIn MITOSIS, the 2 cells that come out of the division (lets call them the daughters), are EXACTLY the same in genetic makeup as the original mother cell. They have the very same DNA and therefore make the same proteins and therefore the cells behave the same. \n\n In MEIOSIS on the other hand, the cells are not the same at all. And in fact, this is the point of meiosis - to make new types of cells. You may know that eggs and sperm are products of meiosis, but you not only get a mixing of genes from your mother (from the egg) and father (from the sperm), but the genes inside the egg and sperm are pre-mixed because of meiosis. Thus, genetic diversity!, and an explanation for why you have traits given to you from your grandmother through your father, even though your father may not have that trait (he carries it in his genes for later mixing). This may be a complicated issue in itself but since we have 2 of every chromosome and therefore 2 of every gene (even before the DNA replication that preceeds mitosis), there's a chance that the 2 copies of the same gene are different, one of which shows up in your father and one which you have that you got from your grandmother throuh your father. The mixing, by the way comes about because after the DNA replicates in preparation for cell division. This is neat and involves chromosomes breaking apart and joining back together. Take a look at the animated movie of meiosis at http://www.biology.yale.edu/animatedMeiosis.nclk - make a point to notice the red and green chromosomes at the beginning and the mixed ones at the end.
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(m)\n\nIn biology, meiosis is the process that transforms one diploid cell into four haploid cells in eukaryotes in order to redistribute the diploid's cell's genome.\n\nMeiosis forms the basis of sexual reproduction and can only occur in eukaryotes. In meiosis, the diploid cell's genome, which is composed of ordered structures of coiled DNA called chromosomes, is replicated once and separated twice, producing four haploid cells each containing half of the original cell's chromosomes. These resultant haploid cells will fertilize with other haploid cells of the opposite gender to form a diploid cell again. The cyclical process of separation by meiosis and genetic recombination through fertilization is called the life cycle. The result is that the offspring produced during germination after meiosis will have a slightly different blueprint which has instructions for the cells to work, contained in the DNA. This allows sexual reproduction to occur.\n\nMeiosis uses many biochemical processes that are similar to those used in mitosis in order to distribute chromosomes among the resulting cells; however the outcome is very different.\n\ngoto the following link for details about meiosis\nhttp://en.wikipedia.org/wiki/Meiosis
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Mendel's law of independent assortment basically says that each chromosome pair will separate during meiosis individually, regardless of whether the chromosome originated maternally or paternally.  So for example, if there are two pairs of chromosomes, 1 and 2, and each have a maternal and paternal copy (1M, 1P, 2M, and 2P), pairs 1 and 2 will segregate without input from the other pair.  So during meiosis, when the a haploid cell is formed with only one chromosome copy, there are many different combinations that can be formed.  The cell could contain 1M/2M, 1M/2P, 1P/2M, or 1P/2P.  It is easy to see how organisms with more chromosome pairs (humans have 23 pairs, 46 total) will produce more combinations, hence diversity among the species.  Hope that helps!
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I'm sorry I don't see a picture of anything. Would you care to edit your question?\n\nMitosis- http://en.wikipedia.org/wiki/Mitosis\nMeiosis- http://en.wikipedia.org/wiki/Meiosis\n\nHope they help.
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Meiosis is specialized cell division (similar to mitosis). Mitosis results in 2 identical daughter cells from a single cell. Meiosis results in 4 daughter cells (which may not be identical) but each daughter cell only has one set of chromosomes, instead of the 2 sets of chromosomes present in the original cell. Each of these daughter cells is called a gamete. In sexual reproduction a male gamete and a female gamete (sperm and egg) fuse. Each contributes a single set of chromosomes so the resulting fused cell (zygote) has two sets like the cells that originally formed the gametes.