Rucete ✏ Biology In a Nutshell
1. What Is Meiosis?
- Meiosis is a type of cell division that reduces the chromosome number by half, producing four haploid cells (n) from one diploid cell (2n).
- It occurs in germ cells and is essential for sexual reproduction.
2. Overview
- Meiosis consists of two divisions:
- Meiosis I: separates homologous chromosomes
- Meiosis II: separates sister chromatids
- Results in four genetically unique haploid cells.
3. Meiosis I: Reduction Division
Prophase I
- Homologous chromosomes pair up (synapsis) and form tetrads.
- Crossing over occurs—exchange of genetic material between homologs.
Metaphase I
- Tetrads align at the metaphase plate.
- Orientation is random → contributes to genetic variation.
Anaphase I
- Homologous chromosomes separate and move toward opposite poles.
- Sister chromatids remain attached.
Telophase I
- Homologous pairs finish moving to opposite poles.
- Nuclear envelope may reform in some species.
Cytokinesis I
- Two haploid cells are formed, each with duplicated chromosomes.
4. Meiosis II: Division of Sister Chromatids
Prophase II
- New spindle forms in each haploid cell.
- Nuclear envelope breaks down (if it had reformed).
Metaphase II
- Chromosomes align at the center (metaphase plate).
Anaphase II
- Sister chromatids separate and move to opposite poles.
Telophase II
- Nuclei reform around the chromosomes.
- Chromosomes decondense.
Cytokinesis II
- Four genetically distinct haploid daughter cells are produced.
In a nutshell
- Produces 4 non-identical haploid cells.
- Ensures genetic diversity via:
- Crossing over (Prophase I)
- Independent assortment (Metaphase I)
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Biology in a nutshell