Lawrence C. Brody, Ph. Featured Content. Introduction to Genomics. Because each chromosome was duplicated during S phase, it now consists of two identical copies called sister chromatids that are attached at a common center point called the centromere. Figure 2: The mitotic spindle white begins to form outside the cell's nucleus.
Important changes also take place outside of the nucleus during prophase. In particular, two structures called centrosomes move to opposite sides of the cell during this phase and begin building the mitotic spindle. The mitotic spindle plays a critical role during the later phases of mitosis as it orchestrates the movement of sister chromatids to opposite poles of the cell Figure 2. After prophase is complete, the cell enters prometaphase.
During prometaphase, the nuclear membrane disintegrates and the mitotic spindle gains access to the chromosomes. During this phase, a protein structure called the kinetochore is associated with the centromere on each sister chromatid.
Stringlike structures called microtubules grow out from the spindle and connect to the sister chromatids at their kinetochores; one microtubule from one side of the spindle attaches to one sister chromatid in each chromosome, and one microtubule from the other side of the spindle attaches to the other sister chromatid Figure 3a.
Figure 3: a Metaphase and b Anaphase. In metaphase a , the microtubules of the spindle white have attached and the chromosomes have lined up on the metaphase plate.
During anaphase b , the sister chromatids are pulled apart and move toward opposite poles of the cell. Figure Detail. After metaphase is complete, the cell enters anaphase. During anaphase, the microtubules attached to the kinetochores contract, which pulls the sister chromatids apart and toward opposite poles of the cell Figure 3c.
At this point, each chromatid is considered a separate chromosome. Figure 4: During telophase, two nuclear membranes form around the chromosomes, and the cytoplasm divides. Finally, once anaphase is complete, the cell enters the last stage of the division process — telophase. During telophase, the newly separated chromosomes reach the mitotic spindle and a nuclear membrane forms around each set of chromosomes, thus creating two separate nuclei inside the same cell.
As Figure 4 illustrates, the cytoplasm then divides to produce two identical cells. The information on this site should not be used as a substitute for professional medical care or advice. Contact a health care provider if you have questions about your health. How do cells divide? From Genetics Home Reference. Mitosis and meiosis, the two types of cell division.
Topics in the How Genes Work chapter What are proteins and what do they do? Developing the Chromosome Theory. Meiosis, Genetic Recombination, and Sexual Reproduction.
Mitosis and Cell Division. Genetic Mechanisms of Sex Determination. Sex Chromosomes and Sex Determination. Sex Chromosomes in Mammals: X Inactivation. Sex Determination in Honeybees. Citation: O'Connor, C. Nature Education 1 1 The five phases of mitosis and cell division tightly coordinate the movements of hundreds of proteins. How did early biologists unravel this complex dance of chromosomes?
Aa Aa Aa. Mitosis Occupies a Portion of the Cell Cycle. Figure 2. Figure 1. Figure Detail. Figure 3. Ascaris megalocephala bivalens, as drawn by Boveri in The figure shows chromosomes in the middle of the dividing cell, as well as the spindle, two centrosomes, and two centrioles within each centrosome. Note that the cytoplasm is perceived as being structured. Figure 6. Figure 5. Figure 7. Figure 8. Figure Telophase and Cytokinesis. References and Recommended Reading Cheeseman, I.
Article History Close. Share Cancel. Revoke Cancel. Keywords Keywords for this Article. Save Cancel. Flag Inappropriate The Content is: Objectionable. Flag Content Cancel. Email your Friend. Submit Cancel. This content is currently under construction. Explore This Subject. Chromosome Analysis. Chromosome Structure.
Mutations and Alterations in Chromosomes. Chromosome Number. Chromosome Theory and Cell Division.
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