Mitosis & Meiosis

Cheatsheet Content

### Mitosis: Cell Duplication Mitosis is a type 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. #### Key Characteristics: - **Parent Cell:** Diploid (2n) - **Daughter Cells:** 2, Diploid (2n) - **Genetic Content:** Identical to parent cell - **Purpose:** Growth, repair, asexual reproduction - **Stages:** Prophase, Metaphase, Anaphase, Telophase (PMAT) #### Stages of Mitosis: 1. **Interphase:** Cell grows, DNA replicates (becomes sister chromatids). 2. **Prophase:** Chromosomes condense, nuclear envelope breaks down, spindle fibers form. 3. **Metaphase:** Chromosomes align at the metaphase plate (equator of the cell). 4. **Anaphase:** Sister chromatids separate and move to opposite poles of the cell. 5. **Telophase:** Chromosomes decondense, nuclear envelopes reform, spindle fibers disappear. 6. **Cytokinesis:** Cytoplasm divides, forming two distinct daughter cells. ### Meiosis: Genetic Diversity Meiosis is a type of cell division that reduces the number of chromosomes in the parent cell by half and produces four gamete cells. This process is required to produce egg and sperm cells for sexual reproduction. #### Key Characteristics: - **Parent Cell:** Diploid (2n) - **Daughter Cells:** 4, Haploid (n) - **Genetic Content:** Genetically different from parent cell and each other - **Purpose:** Sexual reproduction, genetic diversity - **Stages:** Meiosis I (PMAT I) and Meiosis II (PMAT II) #### Stages of Meiosis I: 1. **Interphase:** Cell grows, DNA replicates. 2. **Prophase I:** Chromosomes condense, homologous chromosomes pair up (synapsis), **crossing over** occurs (exchanging genetic material). Nuclear envelope breaks down. 3. **Metaphase I:** Homologous pairs align at the metaphase plate. 4. **Anaphase I:** Homologous chromosomes separate and move to opposite poles. Sister chromatids remain attached. 5. **Telophase I:** Chromosomes may decondense, nuclear envelopes may reform. Cytokinesis usually follows, forming two haploid cells, each with duplicated chromosomes. #### Stages of Meiosis II: (Similar to Mitosis, but starting with haploid cells) 1. **Prophase II:** Chromosomes condense (if decondensed), nuclear envelope breaks down. 2. **Metaphase II:** Sister chromatids align at the metaphase plate. 3. **Anaphase II:** Sister chromatids separate and move to opposite poles. 4. **Telophase II:** Chromosomes decondense, nuclear envelopes reform. 5. **Cytokinesis:** Cytoplasm divides, resulting in four haploid daughter cells, each with unduplicated chromosomes. ### Key Differences | Feature | Mitosis | Meiosis | | :-------------------- | :------------------------------------ | :---------------------------------------- | | **Number of Divisions** | 1 | 2 | | **Daughter Cells** | 2 diploid (2n) | 4 haploid (n) | | **Genetic Identity** | Identical to parent | Genetically diverse | | **Chromosome No.** | Stays the same (2n $\to$ 2n) | Halved (2n $\to$ n) | | **Purpose** | Growth, repair, asexual reproduction | Sexual reproduction, genetic variation | | **Crossing Over** | Does not occur | Occurs in Prophase I | | **Homologous Pairing**| No | Yes, in Prophase I |