Phases of Meiosis

Introduction to Meiosis

Meiosis, also known as reduction division, is the process of cell division that produces gametes (sex cells like sperm and egg cells).
Meiosis consists of two stages of cell division: Meiosis I and Meiosis II.

Prophase I
- Begins with a diploid cell.
- Chromatin contains two uncoiled chromosome sets (from each parent).
- DNA replicates and condenses into X-shaped chromosomes.
- Chromosomes pair up (synapsis) with homologous chromosomes, forming a tetrad (4 chromatids).
- Crossing over occurs, exchanging alleles between chromatids, leading to genetic variety.
- Nuclear membrane disappears; centrioles move to opposite ends; spindle fibers form.
Metaphase I
- Homologous chromosomes line up at the equator.
- Chromosomes attach to spindle fibers from opposite poles.
Anaphase I
- Homologous chromosomes in tetrads separate and move to opposite poles.
Telophase I
- Each pole has one chromosome from each homologous pair.
- Chromosomes consist of non-identical sister chromatids due to crossing over.
- Nuclear membrane reforms; spindle fibers disappear; cytokinesis occurs.
- Ends with two genetically different haploid daughter cells.

Prophase II
- No DNA replication occurs before.
- Nuclear membrane disappears; spindle fibers form from centrioles.
Metaphase II
- Chromosomes line up at the equator.
- Attach to spindle fibers from both poles.
Anaphase II
- Sister chromatids separate and move to opposite poles, now called chromosomes.
Telophase II
- Spindle fibers disappear; nuclear membranes reform; cytokinesis occurs.
- Results in four genetically different haploid daughter cells.

Meiosis starts with a diploid cell and produces genetically different haploid gametes.
Consists of two stages: Meiosis I (separation of homologous chromosomes) and Meiosis II (separation of sister chromatids).
Crossing over during Prophase I results in genetic variation in gametes.
All gametes produced by meiosis are haploid.