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Meiosis
Meiosis is a specialized type of cell division that occurs in germ cells (cells involved in sexual reproduction) to produce haploid gametes (sperm and eggs) with half the number of chromosomes as the parent cell. It involves two rounds of division, known as meiosis I and meiosis II, resulting in the formation of four non-identical daughter cells.
Here is a summary of the stages of meiosis:
Meiosis I:
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Prophase I: This is the longest phase of meiosis. Chromatin condenses into visible chromosomes, and homologous chromosomes come together to form pairs, a process known as synapsis. Each pair of homologous chromosomes aligns and forms a structure called a tetrad. Crossing over can occur during this stage, where genetic material is exchanged between homologous chromosomes, increasing genetic diversity.
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Metaphase I: Tetrads align at the equatorial plane of the cell. The orientation of each pair of homologous chromosomes is random, which further contributes to genetic variation.
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Anaphase I: Homologous chromosomes separate and move toward opposite poles of the cell. Sister chromatids remain attached at their centromeres.
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Telophase I: Chromosomes reach the poles of the cell, and the nuclear envelope may reform around each set of chromosomes. Cytokinesis then follows, dividing the cytoplasm to form two daughter cells.
Meiosis II: 5. Prophase II: The nuclear envelope breaks down, and the spindle apparatus forms. Each daughter cell from meiosis I now contains half the number of chromosomes but still consists of sister chromatids.
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Metaphase II: Sister chromatids align at the equatorial plane of each daughter cell.
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Anaphase II: Sister chromatids separate and move toward opposite poles of the cells.
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Telophase II: Chromosomes reach the poles, and the nuclear envelope reforms around each set of chromosomes.
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Cytokinesis II: The cytoplasm divides, resulting in the formation of four non-identical haploid daughter cells.
The four daughter cells produced at the end of meiosis are genetically distinct from each other and from the parent cell. Meiosis generates genetic diversity through the random assortment of chromosomes during metaphase I and the exchange of genetic material through crossing over during prophase I.
The haploid daughter cells, which contain half the number of chromosomes as the parent cell, can later fuse with another haploid cell during fertilization to restore the diploid chromosome number in the resulting zygote.
Meiosis plays a crucial role in sexual reproduction by ensuring the production of gametes with genetic diversity. It allows for the shuffling and recombination of genetic material, contributing to the variation observed in offspring.