what is the significance of what happens in prophase-1 of meiosis?
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Prophase I\nIn the leptotene stage, the cell's genetic material, which is normally in a loosely arranged pile known as chromatin, condenses into visible threadlike structures. Along the thread, centromeres are visible as small beads of tightly coiled chromatin. Recall that centromeres are connection sites between sister chromatids, which are not yet distinguishable. As the chromatin becomes progressively ordered and visible, homologous chromosomes find each other and bind together. In this process, called synapsis, a protein structure called the synaptonemal complex attaches the homologous chromosomes tightly together all along their lengths.\n\nThe zygotene stage sees the completion of synapsis. The paired homologous chromosomes are said to be bivalent. They may also be referred to as a tetrad, a reference to the four sister chromatids. During this stage, one percent of DNA that wasn't replicated during S phase is replicated. The significance of this cleanup act is unclear.\n\nThe pachytene stage heralds crossing over. Nonsister chromatids of homologous chromosomes exchange segments of genetic information. Because the chromosomes cannot be distinguished in the synaptonemal complex, the actual act of crossing over is not perceivable through the microscope.\n\nDuring the diplotene stage, the synaptonemal complex degrades. Homologous chromosomes fall apart and begin to repel each other. The chromosomes themselves uncoil a bit, allowing some transcription of DNA. They are held together by virtue of recombination nodules, betraying the sites of previous crossing over, the chiasmata.\n\nChromosomes recondense during the diakinesis stage. Sites of crossing over entangle together, effectively overlapping, making chiasmata clearly visible. In general, every chromosome will have crossed over at least once. The nucleoli disappears and the nuclear membrane disintegrates into vesicles.\n\nDuring these stages, centrioles are migrating to the two poles of the cell. These centrioles, which were duplicated during interphase, function as microtubule coordinating centers. Centrioles sprout microtubules, essentially cellular ropes and poles, during crossing over. They invade the nuclear membrane after it disintegrates, attaching to the chromosomes at the kinetochore. The kinetochore functions as a motor, pulling the chromosome along the attached microtubule toward the originating centriole, like a train on a track. There are two kinetochores on each tetrad, one for each centrosome. Prophase I is the longest phase in meiosis.\n\nMicrotubules that attach to the kinetochores are known as kinetochore microtubules. Other microtubules will interact with microtubules from the opposite centriole. These are called nonkinetochore microtubules
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1.  It's meiosis not meisosis\n\n2. sure just go to en.wikipedia.org and on the left look up meiosis\n\n3.  or just go to this link.  http://en.wikipedia.org/wiki/Meiosis
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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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It is definitely the chromosomes that divide in both mitosis and meiosis. However, the whole cells divides so # 1 sounds like the right answer. Did you ask in class? I am glad you are asking here , but you really should ask your teacher.
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In 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\nIn metaphase, as kinetochore microtubules from both centrioles attach to their respective kinetochores, the homologous chromosomes align equidistant above and below an imaginary equatorial plane, due to continuous counterbalancing forces exerted by the two kinetochores of the bivalent. Because of independent assortment, the orientation of the bivalent along the plane is random. Maternal or paternal homologues may point to either pole.
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During prophase 1 of meiosis, the chromosomes have duplicated and have joined with their homologous pair to form a 4 stranded tetrad.\n\nBecause you get one chromosome in each homologous pair from your mother and one from your father, although they code for the same concepts, they may code slightly differently (ie blue eyes vs brown eyes).\n\nTo exchange genetic material, during prophase one the two chromatids closest together in the tetrad (one from each mom and dad- the outer two are too far away to do this, so they remain untouched) "cross over".  Literally, the ends of the chromatids cross each other and bits of the chromosomes break off of one and reattach on the other, giving genetic variability.\n\nOk, so for example: the chromosome your mother gave you coded for blue eyes, blonde hair, curly hair, and long fingers.\nThe chromosome from your father codes for the same principles, just differently- say brown eyes, red hair, straight hair and short fingers.\n\nSo crossing over between these two occur in prophase 1, and some codes are swapped.\n\nNow we have a tetrad (4 chromatids) that code for the following.\n(We'll say the chromosome from mother is on the left and from father is on the right)\nStarting with the leftmost and going to the rightmost:\nChromatid 1 codes for: \n-blue eyes, blonde hair, curly hair, and long fingers\nChromatid 2 codes for:\n-blue eyes, brown hair, curly hair, and short fingers.\nChromatid 3 codes for:\n-brown eyes, blonde hair, straight hair, and long fingers\nChromatid 4 codes for:\n-brown eyes, brown hair, straight hair and short fingers.\n\nSo now we have the genetic variability, and 4 completely unique chromatids, that are still homologous pairs, just giving us four different codings for the same traits.\n\nHope this helps.
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Meiosis Tutorial \nDNA replication precedes the start of meiosis I. During prophase I, homologous chromosomes pair and form synapses, a step unique to meiosis. The paired chromosomes are called bivalents, and the formation of chiasmata caused by genetic recombination becomes apparent. Chromosomal condensation allows these to be viewed in the microscope. Note that the bivalent has two chromosomes and four chromatids, with one chromosome coming from each parent. The nuclear membrane disappears. One kinetochore forms per chromosome rather than one per chromatid, and the chromosomes attached to spindle fibers begin to move. Bivalents, each composed of two chromosomes (four chromatids) align at the metaphase plate. The orientation is random, with either parental homologue on a side. This means that there is a 50-50 chance for the daughter cells to get either the mother's or father's homologue for each chromosome.Chiasmata separate. Chromosomes, each with two chromatids, move to separate poles. Each of the daughter cells is now haploid (23 chromosomes), but each chromosome has two chromatids. Meiosis Tutorial \nA review of Meiosis \nComparing Meiosis and Mitosis\nChromosome behavior \nMitosis: Homologous chromosomes independent \nMeiosis: Homologous chromosomes pair forming bivalents until anaphase I \nChromosome number- reduction in meiosis \nmitosis- identical daughter cells \nmeiosis- daughter cells haploid \nGenetic identity of progeny: \nMitosis: identical daughter cells \nMeiosis: daughter cells have new assortment of parental chromosomes \nMeiosis: chromatids not identical, crossing ove \nMeiotic errors\nNondisjunction- homologues don't separate in meiosis 1 \nresults in aneuploidy \nusually embryo lethal \nTrisomy 21, exception leading to Downs syndrome \nSex chromosomes \nTurner syndrome: monosomy X \nKlinefelter syndroms: XXY \nTranslocation and deletion: transfer of a piece of one chromosome to another or loss of fragment of a chromosome. \n\nMitosis, Meiosis, and Ploidy\nMitosis can proceed independent of ploidy of cell, homologous chromosomes behave independently \nMeiosis can only proceed if the nucleus contains an even number of chromosomes (diploid, tetraploid). \nTrisomy 21 does not prevent meiosis
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"A" is the answer.  It happens in prophase of meiosis 1 and it does exactly what choice "A" states.  The rest of the choices happen during meiosis as well, but do not explain the importance of crossing over.
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The beginning of somatic cell division or mitosis is called prophase. In early prophase, the centrosomes move toward opposite poles of the cell, organizing the spindle microtubules between them. The sister chromatids become visible in the nucleus as they condense.In late prophase, the nuclear membrane breaks down and some of the spindle microtubules attach to the sister chromatids. The microtubules pull the chromatid pairs to the midline of the cell, or metaphase plate.The chromatids remain lined up between the poles of the cell during metaphase.Anaphase begins when the pairs of sister chromatids separate. The separated chromatids are now called chromosomes, and move toward the poles of the cell.The chromosomes arrive at the poles in telophase, and new nuclear membranes form around them.Division of the cytoplasmic components is called cytokinesis.In animal cells, cytokinesis occurs when a ring of actin and myosin filaments constricts the plasma membrane at the equator. Eventually, the parent cell is divided into two cells.Meiosis I-Prophase I-In the leptotene stage, the cell's genetic material, which is normally in a loosely arranged pile known as chromatin, condenses into visible threadlike structures. Along the thread, centromeres are visible as small beads of tightly coiled chromatin. Recall that centromeres are connection sites between sister chromatids, which are not yet distinguishable. As the chromatin becomes progressively ordered and visible, homologous chromosomes find each other and bind together. In this process, called synapsis, a protein structure called the synaptonemal complex attaches the homologous chromosomes tightly together all along their lengths.The zygotene stage sees the completion of synapsis. The paired homologous chromosomes are said to be bivalent. They may also be referred to as a tetrad, a reference to the four sister chromatids. During this stage, one percent of DNA that wasn't replicated during S phase is replicated. The significance of this cleanup act is unclear.The pachytene stage heralds crossing over. Nonsister chromatids of homologous chromosomes exchange segments of genetic information. Because the chromosomes cannot be distinguished in the synaptonemal complex, the actual act of crossing over is not perceivable through the microscope.During the diplotene stage, the synaptonemal complex degrades. Homologous chromosomes fall apart and begin to repel each other. The chromosomes themselves uncoil a bit, allowing some transcription of DNA. They are held together by virtue of recombination nodules, betraying the sites of previous crossing over, the chiasmata.Chromosomes recondense during the diakinesis stage. Sites of crossing over entangle together, effectively overlapping, making chiasmata clearly visible. In general, every chromosome will have crossed over at least once. The nucleoli disappears and the nuclear membrane disintegrates into vesicles.During these stages, centrioles are migrating to the two poles of the cell. These centrioles, which were duplicated during interphase, function as microtubule coordinating centers. Centrioles sprout microtubules, essentially cellular ropes and poles, during crossing over. They invade the nuclear membrane after it disintegrates, attaching to the chromosomes at the kinetochore. The kinetochore functions as a motor, pulling the chromosome along the attached microtubule toward the originating centriole, like a train on a track. There are two kinetochores on each tetrad, one for each centrosome. Prophase I is the longest phase in meiosis.Microtubules that attach to the kinetochores are known as kinetochore microtubules. Other microtubules will interact with microtubules from the opposite centriole. These are called nonkinetochore microtubules.Metaphase I-As kinetochore microtubules from both centrioles attach to their respective kinetochores, the homologous chromosomes align equidistant above and below an imaginary equatorial plane, due to cont
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two cell divisions.... one for meiosis 1 and one for meiosis 2
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During prophase. But it actually doesn't happen in all organisms. Yeast for example has a nuclear duplication and division without ever breaking down the nuclear membrane.
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Phases of mitosis\n \nThe cell cycle.The mitotic phase is a relatively short action-packed period of the cell cycle. It alternates with the much longer interphase, where the cell prepares itself for division. Interphase is divided into three phases, G1 (first gap), S (synthesis), and G2 (second gap). During all three phases, the cell grows by producing proteins and cytoplasmic organelles. However, chromosomes are replicated only during the S phase. Thus, a cell grows (G1), continues to grow as it duplicates its chromosomes (S), grows more and prepares for mitosis (G2), and divides (M).\n\nMitosis is a continual and dynamic process. For purposes of description, however, mitosis is conventionally broken down into five subphases: prophase, prometaphase, metaphase, anaphase, and telophase.\n\n[edit]\nProphase\n \nProphase: The two round objects above the nucleus are the centrosomes. Note the condensed chromatin.Main article: Prophase \nNormally, the genetic material in the nucleus is in a loosely bundled coil called chromatin. At the onset of prophase, chromatin condenses together into a highly ordered structure called a chromosome. Since the genetic material has already been duplicated earlier in S phase, the chromosomes have two sister chromatids, bound together at the centromere by the protein cohesin. Chromosomes are visible at high magnification through a light microscope.\n\nJust outside the nucleus are two centrosomes. Each centrosome, which was replicated earlier independent of mitosis, acts as a coordinating center for the cell's microtubules. The two centrosomes sprout microtubules (which may be thought of as cellular ropes or poles) by polymerizing free-floating tubulin protein. By repulsive interaction of these microtubules with each other, the centrosomes push themselves to opposite ends of the cell (although new research has shown that there might be a mechanism inside the centromeres that also grab the microtubules and pull the chromatids apart). The network of microtubules is the beginning of the mitotic spindle.\n\nSome centrosomes contain a pair of centrioles that may help organize microtubule assembly, but they are not essential to formation of the mitotic spindle. Plant cells that lack centrioles have no trouble undergoing mitosis.\n\n[edit]\nPrometaphase\n \nPrometaphase: The nuclear membrane has degraded, and microtubules have invaded the nuclear space. These microtubules can attach to kinetochores or they can interact with opposing microtubules.Main article: Prometaphase \nThe nuclear envelope dissolves and microtubules invade the nuclear space. This is called open mitosis, and it occurs in most multicellular organisms. Some protists, such as algae, undergo a variation called closed mitosis where the microtubules are able to penetrate an intact nuclear envelope.\n\nEach chromosome forms two kinetochores at the centromere, one attached at each chromatid. A kinetochore is a complex protein structure that is analogous to a ring for the microtubule hook; it is the point where microtubules attach themselves to the chromosome. Although the kinetochore is not fully understood, it is known that it contains a molecular motor. When a microtubule connects with the kinetochore, the motor activates, using energy from ATP to "crawl" up the tube toward the originating centrosome. The kinetochore provides the pulling force necessary to later separate the chromosome's two chromatids.\n\nWhen the spindle grows to sufficient length, kinetochore microtubules begin searching for kinetochores to attach to. A number of nonkinetochore microtubules find and interact with corresponding nonkinetochore microtubules from the opposite centrosome to form the mitotic spindle.CXV\n\nPrometaphase is sometimes considered part of prophase.\n\n[edit]\nMetaphase\n \nMetaphase: The chromosomes have aligned at the metaphase plate.Main article: Metaphase \nAs microtubules find and attach to kinetochores in prometaphase, the centro
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Meiosis reduces a cell from a diploid cell to a haploid cell. This is important because if it didn't reduce a diploid to a haploid cell, when fertilization would occur, chromosomes would double and that is bad. Chromosome number is species based.\n\nSexual reproduction requires meiosis.\n\nMeiosis in stages....\n\nMeiosis1\n\nInterphase-same as interphase usually is. \n\nMeiosis I\nProphase I-crossing over (homologous chromosomes switch nonsister chromatids). Also the mitotic spindle fibers start forming from the aster and the nuclear envelope disappears.\n\nMetaphase I-The chromosomes meet together at the metaphasic plate, longest phase outside of interphase.\n\nAnaphase I-the chromosomes stay together (aka no break at centromere) they just don't pair up anymore. The pairs split, one chromosome going one way, the other going the other way.\n\nTelophase I and Cytokinesis-Nuclear envelope may or may not reform once the cleavage furrow or cell plate occur. Understand cytoplasmic inheritance with this as well.\n\nMeiosis II\n\nProphase (No interphase) II-no duplicaiton of chromosomes. The mitotic spindles form again\n\nMetaphase II-Everything goes towards the mitotic plate\n\nAnaphase II-The kinetochore spindles, or mitotic spindles, attach to the kinetochores and separate the chromosomes, bringing one chromatid to one end of the cell, another to the other end of the cell.\n\nTelophase II and cytokinesis-four haploid daughter cells are created. Think about it, meiosis I produces two cells, second division creates 4 because each diploid cell produces two haploids.
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This is simple. The interphase is a stage of the cell cycle.\nHere is the article in Wikipedia:\n"Interphase is a phase of the cell cycle, defined only by the absence of cell division. During interphase, the cell obtains nutrients, and duplicates its chromosomes. Most eukaryotic cells spend most of their time in interphase. For example, human skin cells, which divide about once a day, spend roughly 22 hours in interphase. Cells during interphase may or may not be growing. At any given time, even in an area of rapid cell division such as the tip of a plant root, 90 percent of cells are in interphase. Some cells, such as nerve cells, can stay in interphase for decades. The cell grows and replicates its DNA and centrioles. There are 3 parts of interphase: G1 (growth 1 in which the cell creates organelles and begins metabolism), S phase (DNA synthesis in which the chromosomes of the cell are copied) and G2 (growth 2 in which the cell grows in preparation for cell division). Sometimes the cells exit the cell cycles (usually from G1 phase) and enter the G0 phase. In the G0 phase, cells are alive and metabolically active, but do not divide. In this phase cells do not copy their DNA and do not prepare for cell division. Many cells in the human body, including those in heart muscle, eyes, and brain are in the G0 phase. If these cells are damaged they cannot be replaced. Interphase is the step before the mitotic phase, though it is frequently erroneously thought to be part of mitosis. The mitotic phase follows interphase, and begins with prophase.\n\nDuring interphase, the chromosomes are found arranged in the nucleus and appear as a network of long, thin threads, called the chromatin. At some point before prophase begins, the chromosomes begin to replicate themselves to form pairs of identical chromosomes. The deoxyribose nucleic acid (DNA) of the chromosomes is in use only during interphase, when the cell is in a stable and self reliant phase. In prophase the two chromatids are still connected by something called the centromere. The sister chromosomes contract tightly. Meanwhile, the nucleolus and the nuclear envelope break down and disappear, since their components have been sufficiently altered. Outside the nucleus are two centrosomes which sprout microtubules by polymerizing free-floating proteins. The centrosomes push themselves to opposite ends of the cell. The network of microtubules forms the beginning of the mitotic spindle. These spindle fibers become visible. The centrioles separate starting to radiate bundles of fibers, called asters. The spindle fibers run from one centriole to the other, at both poles of the cell. At the onset of prophase, chromatin condenses together into a highly ordered structure called a chromosome."\n---- End of citation ---\n\n\nRegarding the staining of the onion specimen - you do this in order to see the inner parts of the cell at the microscope. There are diferent types of colorations and you use one or other dependeg on what do you want to see (for example some coloration could be used for seing the chromosomes, while other coloration might be better for examining the cell wall).
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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.click here:http://en.wikipedia.org/wiki/Meiosis#History\n\nMitosis is the process by which a cell separates its duplicated genome into two identical halves. It is generally followed immediately by cytokinesis which divides the cytoplasm and cell membrane. This results in two identical daughter cells with a roughly equal distribution of organelles and other cellular components. Mitosis and cytokinesis together is defined as the mitotic (M) phase of the cell cycle, the division of the mother cell into two daughter cells, each the genetic equivalent of the parent cell.\n\nMitosis occurs exclusively in eukaryotic cells. In multicellular organisms, the somatic cells undergo mitosis, while germ cells — cells destined to become sperm in males or ova in females — divide by a related process called meiosis. Prokaryotic cells, which lack a nucleus, divide by a process called binary fission.\n\nBecause cytokinesis usually occurs in conjunction with mitosis, "mitosis" is often used interchangeably with "mitotic phase". However, there are many cells where mitosis and cytokinesis occur separately, forming single cells with multiple nuclei. This occurs most notably among the fungi and slime moulds, but is found in various different groups. Even in animals, cytokinesis and mitosis may occur independently, for instance during certain stages of fruit fly embryonic development.\n\nTranscription is generally believed to cease during mitosis, but epigenetic mechanisms such as bookmarking function during this stage of the cell cycle to ensure that the "memory" of which genes were active prior to entry into mitosis are transmitted to the daughter cells.click here:http://en.wikipedia.org/wiki/Mitosis#Overview
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The following quote is from \n\nhttp://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=pubmed&dopt=Abstract&list_uids=3607844&query_hl=6&itool=pubmed_docsum\n\n"prophase lasted 4.8 hr; metaphase, 0.2 hr; anaphase, 0.06 hr and telophase, 3.3 hr, while the interphase lasted 5.4 hr. In accordance with this, the duration of the whole mitotic process was 8.4 hr."
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that mitosis or meiosis occured.