The sister chromatids are separated simultaneously at their centromeres. The separated chromosomes are then pulled by the spindle to opposite poles of the cell. Anaphase ensures that each daughter cell receives an identical set of chromosomes, and it is followed by the fifth and final phase of mitosis, known as telophase. Further Exploration Concept Links for further exploration cell division chromosome centromere meiosis DNA cytokinesis spindle fibers metaphase telophase.
Related Concepts 9. You have authorized LearnCasting of your reading list in Scitable. Do you want to LearnCast this session? This article has been posted to your Facebook page via Scitable LearnCast. Change LearnCast Settings. Shorter fibers also emanate from the mitotic spindle but are not attached to chromosomes.
At the start of metaphase I , microtubules emerge from the spindle and attach to the kinetochore near the centromere of each chromosome. In particular, microtubules from one side of the spindle attach to one of the chromosomes in each homologous pair, while microtubules from the other side of the spindle attach to the other member of each pair.
With the aid of these microtubules, the chromosome pairs then line up along the equator of the cell, termed the metaphase plate Figure 2. Anaphase I. Figure 3: During anaphase I, the homologous chromosomes are pulled toward opposite poles of the cell. The chromosome at right is moving toward the right-hand mitotic spindle.
The chromosome is mostly orange, but the lower region of the left chromatid is green. A second pair of chromosomes exhibiting the same pattern of coloration on their arms is shown below the topmost pair, mirroring the movements of the chromosomes above.
During anaphase I, the microtubules disassemble and contract; this, in turn, separates the homologous chromosomes such that the two chromosomes in each pair are pulled toward opposite ends of the cell Figure 3. This separation means that each of the daughter cells that results from meiosis I will have half the number of chromosomes of the original parent cell after interphase.
Also, the sister chromatids in each chromosome still remain connected. As a result, each chromosome maintains its X-shaped structure. Telophase I. Figure 4: Telophase I results in the production of two nonidentical daughter cells, each of which has half the number of chromosomes of the original parent cell.
As the new chromosomes reach the spindle during telophase I , the cytoplasm organizes itself and divides in two. There are now two cells, and each cell contains half the number of chromosomes as the parent cell.
In addition, the two daughter cells are not genetically identical to each other because of the recombination that occurred during prophase I Figure 4.
At this point, the first division of meiosis is complete. The cell now rests for a bit before beginning the second meiotic division. During this period, called interkinesis , the nuclear membrane in each of the two cells reforms around the chromosomes.
In some cells, the spindle also disintegrates and the chromosomes relax although most often, the spindle remains intact. It is important to note, however, that no chromosomal duplication occurs during this stage. What happens during meiosis II? Prophase II. As prophase II begins, the chromosomes once again condense into tight structures, and the nuclear membrane disintegrates.
In addition, if the spindle was disassembled during interkinesis, it reforms at this point in time. Metaphase II. Figure 5: During metaphase II, the chromosomes align along the cell's equatorial plate. The events of metaphase II are similar to those of mitotic metaphase — in both processes, the chromosomes line up along the cell's equatorial plate, also called the metaphase plate, in preparation for their eventual separation Figure 5.
Anaphase II. Figure 6: Anaphase II involves separation of the sister chromatids. During anaphase II , microtubules from each spindle attach to each sister chromatid at the kinetochore. The sister chromatids then separate, and the microtubules pull them to opposite poles of the cell. As in mitosis, each chromatid is now considered a separate chromosome Figure 6. This means that the cells that result from meiosis II will have the same number of chromosomes as the "parent" cells that entered meiosis II.
Telophase II. Figure 7: Telophase II results in the production of four daughter cells. Finally, in telophase II , nuclear membranes reform around the newly separated chromosomes, which relax and fade from view.
As soon as the cytoplasm divides, meiosis is complete. There are now four daughter cells — two from each of the two cells that entered meiosis II — and each daughter cell has half the normal number of chromosomes Figure 7. Each also contains new mixtures of genes within its chromosomes, thanks to recombination during meiosis I. Why is meiosis important? More about meiosis. Genes are packaged differently in mitosis and meiosis — but what is the effect of this difference?
What else can go wrong with chromosomes in meiosis? Meiosis is important because it ensures that all organisms produced via sexual reproduction contain the correct number of chromosomes. Meiosis also produces genetic variation by way of the process of recombination.
Later, this variation is increased even further when two gametes unite during fertilization, thereby creating offspring with unique combinations of DNA. This constant mixing of parental DNA in sexual reproduction helps fuel the incredible diversity of life on Earth.
Watch this video for a summary of meiosis. Key Questions How did sexual reproduction evolve? What happens when meiosis goes wrong? Key Concepts chromosome meiosis haploid diploid recombination. Topic rooms within Genetics Close. No topic rooms are there. Browse Visually. Other Topic Rooms Genetics. Student Voices. Creature Cast. Simply Science. Green Screen. Green Science.
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