![]() Or more of your copyrights, please notify us by providing a written notice (“Infringement Notice”) containing If you believe that content available by means of the Website (as defined in our Terms of Service) infringes one ![]() After the M phase is the separation of the cytoplasm, known as cytokinesis, which results in two distinct daughter cells. This is followed by the reformation of the nuclear envelope, uncoiling of the DNA, and disappearance of the spindle fibers. During the last phase of mitosis, telophase, the two sets of chromosomes reach the opposite poles of the cell. ![]() Next, during anaphase, the centromeres holding the sister chromatids together are divided and the sister chromatids are pulled apart by the spindle fibers to opposite poles of the diving cell. The spindle fibers are completely formed and are attached to each sister chromatid of the chromosomes. In the next phase, metaphase, the chromosomes line up along the metaphasic plate. In prophase, each chromosome becomes condensed and more visible, and there is the breakdown of the nuclear membrane and appearance of spindle fibers. Mitosis has four sequential stages: prophase, metaphase, anaphase, and telophase. This allows for the separation of each sister chromatid into its respective daughter cell. The division of the centromeres occurs during anaphase. Prophase is generally considered to be over when the chromosomes are fully condensed, clear, and the nuclear membrane is gone or almost gone.Centromeres are the structures at the center of each chromosome that hold the sister chomatids together. The centrioles, and asters, are at opposite ends of the cell and the thin protein spindle fibers are reaching out and attaching to the centromeres of each chromosome from opposite directions. The chromosomes are very distinct, easy to recognize and have clear "arms" composed of the two parts of the sister chromatids. Late prophase - the nuclear membrane and the nucleolus finally vanishes completely. In animal cells a system of thin protein fibers begins to radiate out from the centrioles forming a pattern in the cytoplasm of the cell that looks like a star or aster. The pairs of centrioles continue to move around the almost vanished nucleus to opposite sides of the cell. The location of the centromere along the length of the chromosome and chromatids is a distinctive characteristic of many chromosomes, and can sometimes be used (with other factors) to identify them. Each chromosome consists of two identical halves called chromatids, that are connected and held together by a constriction called a centromere. Mid-prophase - the chromatin threads are now condensed enough to be distinguished as individual chromosomes. In animal cells (mostly), a double pair of short, rod-like structures called centrioles, appear, separate and begin to move to opposite sides of the cell, outside the vanishing nucleus. The nucleolus also becomes indistinct and begins to vanish. It is usually not possible to follow individual threads, but the condensation of the material into individual units is becoming obvious. This is generally taken as the beginning of prophaseĮarly prophase - the nuclear membrane becomes more and more indistinct and the chromatin fibers become more and more packaged and condensed. The molecules of DNA become associated with more and more histone proteins and package themselves into higher and higher degrees of structure. ProphaseĪs the cell moves out of G 2 and into M the granular nature of the nucleus begins to change and condense into a series of fine threads. Nuclear division or karyokinesis is a continuous process, however, and there are no artificial divisions in actively growing cells. Early microscopists found it convenient to subdivide the nuclear division of cells into stages that were easily seen under the microscope using colored dyes that stained the chromosomes and some of the other participants. With the right techniques, the next stage in the cell cycle, mitosis (M), can be observed using a good light microscope. The three main phases of a single cell cycle are: interphase, nuclear division and cytoplasmic division.
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