Meiosis is a type of cell division that produces sex cells or gametes, such as eggs in females and sperm in males. Meiosis can be divided into two main stages: meiosis I and meiosis II. Both stages follow the same stages as mitosis, which are prophase, metaphase, anaphase, and telophase.
The stages of meiosis I are as follows:
- Interphase: The DNA in the cell is copied resulting in two identical full sets of chromosomes.
- Prophase I: Chromosomes condense, nuclear membrane dissolves, homologous chromosomes form bivalents, crossing over occurs.
- Metaphase I: Spindle fibers from opposing centrosomes connect to bivalents (at centromeres) and align them along the middle of the cell.
- Anaphase I: Spindle fibers contract and split the bivalent, homologous chromosomes move to opposite poles of the cell.
- Telophase I and cytokinesis: Chromosomes decondense, nuclear membrane may reform, cell divides (cytokinesis) to form two haploid daughter cells.
The stages of meiosis II are as follows:
- Prophase II: Chromosomes condense, nuclear membrane dissolves, centrosomes move to opposite poles (perpendicular to before).
- Metaphase II: Chromosomes line up in single file along the equator of the cell.
- Anaphase II: Sister chromatids are pulled to opposite poles of the equator.
- Telophase II and cytokinesis: This stage is the same as telophase I, and the cell divides to form four haploid daughter cells.
It is important to note that meiosis I is a reduction division, which reduces the number of chromosomes from diploid to haploid, while meiosis II is equational, meaning that the number of chromosomes remains the same.