meiosis I

Definition

Target type: biologicalprocess

The first meiotic nuclear division in which homologous chromosomes are paired and segregated from each other, producing two haploid daughter nuclei. [GOC:dph, GOC:jl, GOC:mtg_cell_cycle, PMID:9334324]

Meiosis I is the first division of meiosis, a specialized type of cell division that occurs in sexually reproducing organisms to produce gametes (sperm and egg cells). It involves the separation of homologous chromosomes, resulting in two daughter cells, each with half the number of chromosomes as the original cell. The process can be divided into four main stages: Prophase I, Metaphase I, Anaphase I, and Telophase I.

**Prophase I:**
- **Leptotene:** Chromosomes begin to condense and become visible.
- **Zygotene:** Homologous chromosomes pair up, forming synapsis.
- **Pachytene:** Crossing over occurs between non-sister chromatids of homologous chromosomes, exchanging genetic material.
- **Diplotene:** Homologous chromosomes begin to separate, remaining attached at chiasmata, the points where crossing over occurred.
- **Diakinesis:** Chromosomes condense further, and the nuclear envelope breaks down.

**Metaphase I:**
- Homologous chromosome pairs line up along the metaphase plate, with centromeres facing opposite poles.

**Anaphase I:**
- Homologous chromosomes are pulled apart to opposite poles by spindle fibers.
- Sister chromatids remain attached at their centromeres.

**Telophase I:**
- Chromosomes reach the poles, and the cytoplasm divides, forming two daughter cells.
- Each daughter cell contains half the number of chromosomes as the original cell, but each chromosome still consists of two sister chromatids.

Meiosis I reduces the number of chromosomes by half, ensuring that the offspring inherit one set of chromosomes from each parent. The genetic diversity generated by crossing over during prophase I contributes to the genetic variation within a population.'
"

Proteins (2)

Compounds (35)