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What Is Meiosis?Meiosis is the formation of gametes; the sex cells used in sexual reproduction (egg and sperm cells). | Usually, during interphase, body cells are diploid cells; they contain a full set of chromosomes (2n). Gametes are haploid (n). Each parent's gametes contain half the genetic material needed, so when a gamete from each parent fuse together, the offspring has a full set of genetic material (2n); half from each parent. |
The Stages of Meiosis1) Interphase | DNA within the cell is duplicated. | 2n 4n | 2) Prophase I | Chromosomes form homologous pairs (tetrads), and crossing over occurs, where certain genes from each chromosome physically interact and swap over. | 4n | 3) Metaphase I | Tetrads line up at the equator of the cell. | 4n | 4) Anaphase I | Spindle fibers pull 1 chromosome from each tetrad to opposite poles of the cell. | 4n | 5) Telophase I | A cleavage furrow forms, which pinches the cell in the middle. | 4n | 6) Cytokinesis | The cell divides into 2 daughter cells. | 4n 2n | 7) Prophase II | The reformed nuclear envelope breaks down. | 2n | 8) Metaphase II | Chromosomes line up at the cell's equator. | 2n | 9) Anaphase II | Each chromosome's sister chromatids are pulled to opposite poles of the cell by spindle fibers. | 2n | 10) Telophase II | A cleavage furrow forms. | 2n | 11) Cytokinesis | Each daughter cell divides into 2 cells, forming a total of 4 haploid cells for the whole process. | 2n n |
| | What Causes Genetic Variation? Independent assortment, which occurs when chromosomes randomly line up at the equator. | Crossing over, during prophase I, where genetic material is swapped by chromatids. | Random fertilisation. During sexual reproduction, only one sperm will fertilise one egg, meaning it is random chance which combination of genetic information will be present in the parents' gametes. |
How Are Mitosis and Meiosis Different?Differences: | Mitosis | Meiosis | Number of cell divisions | 1 | 2 | Number of daughter cells | 2 | 4 | Genetic composition of daughter cells | 2n | n | Role in animals | Tissue growth, asexual reproduction | Formation of gametes (for sexual reproduction) |
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this is so outragous i cryed
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