Help about the Cell Cycle and Meiosis?
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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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remember the phases in meiosis (in order) :Prophase, Metaphase, anaphase, telephase (pmat)\nMitosis\nI  INTRODUCTION \n\nMitosis, process in which a cell’s nucleus replicates and divides in preparation for division of the cell. Mitosis results in two cells that are genetically identical, a necessary condition for the normal functioning of virtually all cells. Mitosis is vital for growth; for repair and replacement of damaged or worn out cells; and for asexual reproduction, or reproduction without eggs and sperm.\n\nAll multicellular animals, plants, fungi, and protists, which begin life as single cells, carry out mitosis to develop into complex organisms containing billions of cells. Mitosis continues in full-grown organisms as a means of maintaining the organism—replacing dying skin cells, for example, or repairing damaged muscle cells. In the cells of the adult human body, mitosis occurs about 25 million times per second. Multicellular organisms such as sea stars, sea anemones, fungi, and certain plants rely on mitosis for asexual reproduction at particular stages in their life cycles, and mitosis is the sole mode of reproduction for many single-celled organisms.\n\nII  INTERPHASE \n\nThe life cycle of eukaryotic cells, or cells containing a nucleus, is a continuous process typically divided into three phases for ease of understanding: interphase, mitosis, and cytokinesis. Interphase includes three stages, referred to as G1, S and G2. In G1, a newly formed cell synthesizes materials needed for cell growth. In the S stage, deoxyribonucleic acid (DNA), the genetic material of the cell, is replicated. At this stage, DNA consists of long, thin strands called chromatin. As each strand is replicated, it is linked to its duplicate by a structure known as a centromere. When the S stage is complete, the cell enters a brief stage known as G2, when specialized enzymes correct any errors in the newly synthesized DNA, and proteins involved with the next phase, mitosis, are synthesized. \n\nIII  MITOSIS \n\nMitosis occurs in four steps. In prophase the replicated, linked DNA strands slowly wrap around proteins that in turn coil and condense into two short, thick, rodlike structures called chromatids, attached by the centromere. Two structures called centrioles, both located on one side of the nucleus, separate and move toward opposite poles of the cell. As the centrioles move apart, they begin to radiate thin, hollow, proteins called microtubules. The microtubules arrange themselves in the shape of a football, or spindle, that spans the cell, with the widest part at the center of the cell and the narrower ends at opposite poles. As the spindle forms, the nuclear membrane breaks down into tiny sacs or vesicles that are dispersed in the cytoplasm. Final disintegration of the membrane marks the beginning of metaphase. \n\nIn metaphase, the spindle fibers attach to the chromatids near the centromeres, and tug and push the chromatids so that they line up in the equatorial plane of the cell halfway between the poles. Like two individuals standing back to back at the equator, one chromatid faces one pole of the cell, and its linked partner faces the opposite pole. This precise orientation is necessary in order for the next step, anaphase, to occur. Anaphase begins when the centromeres split, separating the identical chromatids into single chromosomes, which then move along the spindle fibers to opposite poles of the cell. \n\nAs these two identical groups of single chromosomes gather at opposite poles of the cell, telophase begins. A new nuclear membrane forms around each new group of chromosomes. The spindle fibers break down and the newly formed chromosomes begin to unwind. If viewed under a light microscope, the chromosomes appear to fade away. They exist, however, in the form of chromatin, the extended, thin strands of DNA too fine to be seen except with electron microscopes. Mitosis accomplishes replication and division of the nucleus,
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Firstly you should ask the proper ques. The ques. should be like this "What is the difference b/w meosis and mitosis".\n        The answer to your ques. is:-\n       MITOSIS                                       MEOSIS\n* Takes place in somatic                  * Takes place in reproductive\n   cells                                                   cells                                    \n* Produces two cells                         * Produces four haploid cells\n* No crossing over                             * Crossing Over takes place\n*The no. of chromosomes re-           * The no. of chromosomes \n  mains the same after mitosis             is reduced to one-half after\n                                                              meiosis
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In biology, meiosis is the process that allows one diploid cell to divide in a special way to generate haploid cells in eukaryotes. The word "meiosis" comes from the Greek meioun, meaning "to make smaller," since it results in a reduction in chromosome number.\n\nMeiosis is essential for sexual reproduction. It therefore occurs in most eukaryotes, including single-celled organisms. A few eukaryotes, notably the Bdelloid rotifers, have lost the ability to carry out meiosis and acquired the ability to reproduce by parthenogenesis. Meiosis does not occur in archaea or prokaryotes, which reproduce by asexual cell division processes.\n\nDuring meiosis, the genome of a diploid germ cell, which is composed of long segments of DNA called chromosomes, undergoes DNA replication followed by two rounds of division, resulting in haploid cells called gametes. Each gamete contains one complete set of chromosomes, or half of the genetic content of the original cell. These resultant haploid cells can fuse with other haploid cells of the opposite gender or mating type during fertilization to create a new diploid cell, or zygote. Thus, the division mechanism of meiosis is a reciprocal process to the joining of two genomes that occurs at fertilization. Because the chromosomes of each parent undergo genetic recombination during meiosis, each gamete, and thus each zygote, will have a unique genetic blueprint encoded in its DNA. In other words, meiosis is the process that produces genetic variation.\n\nBiochemically, meiosis uses some of the same mechanisms employed during mitosis to accomplish the redistribution of chromosomes. There are several features unique to meiosis, most importantly the pairing and recombination between homologous chromosomes, which enable them to separate from each other.\n\nMeiosis facilitates stable sexual reproduction. Without the halving of ploidy, or chromosome count, fertilization would result in zygotes that have twice the number of chromosomes than the zygotes from the previous generation. Successive generations would have an exponential increase in chromosome count, resulting in an unwieldy genome that would cripple the reproductive fitness of the species. Polyploidy, the state of having three or more sets of chromosomes, also results in developmental abnormalities or lethality.\n\nMost importantly, however, meiosis produces genetic variety in gametes that propagate to offspring. Recombination and independent assortment allow for a greater diversity of genotypes in the population. As a system of creating diversity, meiosis allows a species to maintain stability under environmental changes.
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none\n\n\nyou start with one pair of homologous chromosomes in prophase I of meiosis I.  at metaphase I, these homologues line up across the metaphase plate, and at anaphase, they seperate so that one homologue goes to one pole, and the other homologue goes to the other pole.  after cytokinesis at the end of telophase I, you have one homologue in each cell...that homologue then goes through meiosis II, and at metaphase II, that homologue lines up at the metaphase plate with each sister chromatid facing each pole, and the chromosome is "pulled apart".  Anaphase II pulls the sister chromatids to each pole, and cytokinesis splits the one cell into two....two cells, each containing one sister chromatid of a homologous pair. (although in some text books this is refered to as a single homologue)
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Mitosis, also called karyokinesis, is division of the nucleus and its chromosomes.  It is followed by division of the cytoplasm known as cytokinesis.  Both mitosis and cytokinesis are parts of the life of a cell called the Cell Cycle.  Most of the life of a cell is spent in a non-dividing phase called Interphase.  Interphase includes G1 stage in which the newly divided cells grow in size, S stage in which the number of chromosomes is doubled and appear as chromatin, and G2 stage where the cell makes the enzymes & other cellular materials needed for mitosis.\n\nMitosis has 4 major stages --- Prophase, Metaphase, Anaphase, and Telophase. When a living organism needs new cells to repair damage, grow, or just maintain its condition, cells undergo mitosis.\n\nDuring Prophase, the DNA and proteins start to condense. The two centrioles move toward the opposite end of the cell in animals or microtubules are assembled in plants to form a spindle. The nuclear envelope and nucleolus also start to break up.\n\n\nProphase\n\nDuring Metaphase, the spindle apparatus attaches to sister chromatids of each chromosome. All the chromosomes are line up at the equator of the spindle. They are now in their most tightly condensed form.\n\n\nMetaphase\n\nDuring Anaphase, the spindle fibers attached to the two sister chromatids of each chromosome contract and separate chromosomes which move to opposite poles of the cell.\n\n\nAnaphase\nIn Telophase, as the 2 new cells pinch in half (animal cells) or a cell plate forms (plant cells), the chromosomes become less condensed again and reappear as chromatin. New membrane forms nuclear envelopes and the nucleolus is reformed.
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Meiosis is the type of cell division by which germ cells (eggs and sperm) are produced. Meiosis involves a reduction in the amount of genetic material.\n\nMeiosis comprises two successive nuclear divisions with only one round of DNA replication.\nFour stages can be described for each nuclear division.
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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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Mitosis describes the process by which the nucleus of a cell divides to create two new nuclei, each containing an identical copy of DNA\nMeiosis, is the process by which certain sex cells are created. If you're male, your body uses meiosis to create sperm cells; if you're female, it uses meiosis to create egg cells
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mitosis:the process in cell division by which the nucleus divides, typically consisting of four stages: prophase, metaphase, anaphase and telophase.\n\nmeiosis: (genetics) cell division that produces reproductive cells in sexually reproducing organisms; the nucleus divides into four nuclei each containing half the chromosome number (leading to gametes in animals and spores in plants) \n\nosmosis:Transmission of fluids from one cell into another; foundation of metabolism, led by the concentration of salt within a cell. Water can penetrate cell membranes, and strives to, where the concentration of salt is highest, in order to equalize the salt concentration in the body.
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Both involve prophase, metaphase, anaphase and telophase. Both involve cytokinesis, and lastly DNA is replicated just before cells enter either mitosis or meiosis.
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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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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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Interphase\n\nhttp://www.cellsalive.com/cell_cycle.htm
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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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Check out "mitosis" in a suitable source (Wikipedia, for example).  The process is a bit long to describe here.
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There are actually TWO organelles that play a direct role in the process of cell division.\n\nThe centrioles are the structures that establish the poles during mitosis and meiosis. But don't forget the cytoskeleton, which is hugely important during the cytokinesis part of each process.