Mitosis produces diploid cells by accurately replicating the chromosomes of a diploid parent cell during S phase and then separating the resulting identical sister chromatids equally into two daughter cells during M phase (mitotic phase). This ensures each daughter cell receives a complete diploid set of chromosomes.
Here's a more detailed breakdown:
The Process of Mitosis and Diploid Cell Production
Mitosis is a form of cell division that results in two daughter cells, each having the same number and kind of chromosomes as the parent nucleus, typical of ordinary tissue growth. The critical steps ensuring diploidy are:
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Interphase (Specifically S Phase): Before mitosis begins, the cell undergoes interphase, which includes the S (synthesis) phase. During the S phase, the cell's DNA is replicated. Each chromosome is duplicated, resulting in two identical copies called sister chromatids, joined at the centromere. The cell is technically tetraploid (4n) at this point regarding DNA content, but the number of chromosomes is still considered diploid (2n) because the sister chromatids are still considered one chromosome.
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Prophase: The replicated chromosomes condense and become visible. The mitotic spindle begins to form.
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Metaphase: The chromosomes align along the metaphase plate (the equator of the cell). Each sister chromatid is attached to spindle fibers emanating from opposite poles of the cell.
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Anaphase: The sister chromatids separate, becoming individual chromosomes. These chromosomes are pulled to opposite poles of the cell by the shortening of the spindle fibers. Each pole now has a complete diploid set of chromosomes.
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Telophase: The chromosomes arrive at the poles and begin to decondense. The nuclear envelope reforms around each set of chromosomes, creating two distinct nuclei.
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Cytokinesis: The cytoplasm divides, physically separating the two daughter cells. Each daughter cell now contains a complete diploid set of chromosomes (2n) and is genetically identical to the parent cell.
Importance of Accurate Replication and Segregation
The accuracy of DNA replication during S phase and the precise segregation of sister chromatids during anaphase are crucial for maintaining the diploid state in daughter cells. Errors in these processes can lead to aneuploidy (an abnormal number of chromosomes), which can have serious consequences for the organism, including developmental abnormalities and cancer.
Summary
Mitosis maintains diploidy by duplicating the chromosomes during S phase, creating sister chromatids, and then separating these sister chromatids equally into two daughter cells during M phase. Each daughter cell receives a complete diploid set of chromosomes, identical to the parent cell.
