Meiosis — Core Principles
Core Principles
Meiosis is a specialized cell division process that produces four haploid daughter cells from a single diploid parent cell. It is crucial for sexual reproduction, ensuring the maintenance of a constant chromosome number across generations and generating genetic diversity.
The process involves one round of DNA replication followed by two sequential nuclear divisions: Meiosis I and Meiosis II. Meiosis I is a reductional division where homologous chromosomes pair up (synapsis), exchange genetic material (crossing over), and then separate, reducing the chromosome number by half.
Key stages include Prophase I (Leptotene, Zygotene, Pachytene, Diplotene, Diakinesis), Metaphase I, Anaphase I, and Telophase I. Meiosis II is an equational division, similar to mitosis, where sister chromatids separate.
This results in four genetically unique haploid cells (gametes). Genetic variation arises from crossing over and the independent assortment of homologous chromosomes during Meiosis I. Understanding the changes in chromosome number and DNA content at each stage is vital for NEET.
Important Differences
vs Mitosis
| Aspect | This Topic | Mitosis |
|---|---|---|
| Purpose | Meiosis: Production of gametes/spores; genetic variation; chromosome number reduction. | Mitosis: Growth, repair, asexual reproduction; production of identical somatic cells. |
| Location | Meiosis: Germline cells (gonads). | Mitosis: Somatic cells throughout the body. |
| Number of Divisions | Meiosis: Two (Meiosis I and Meiosis II). | Mitosis: One. |
| Number of Daughter Cells | Meiosis: Four haploid cells. | Mitosis: Two diploid cells. |
| Chromosome Number of Daughter Cells | Meiosis: Half of parent cell (haploid, $n$). | Mitosis: Same as parent cell (diploid, $2n$). |
| Genetic Identity of Daughter Cells | Meiosis: Genetically different from parent cell and each other. | Mitosis: Genetically identical to parent cell and each other. |
| Homologous Chromosome Pairing (Synapsis) | Meiosis: Occurs in Prophase I, forming bivalents. | Mitosis: Does not occur. |
| Crossing Over | Meiosis: Occurs in Prophase I, leading to genetic recombination. | Mitosis: Does not occur. |
| Separation in Anaphase I/Anaphase | Meiosis: Homologous chromosomes separate in Anaphase I; sister chromatids separate in Anaphase II. | Mitosis: Sister chromatids separate in Anaphase. |
| DNA Replication | Meiosis: Occurs once before Meiosis I. | Mitosis: Occurs once before mitosis. |