4.3.6 Meiosis Stages

Stages of Meiosis

Meiosis I: Reduction Division

1. Prophase I

• Chromosomes condense, becoming visible.
• Homologous chromosomes pair up to form bivalents.
• Crossing over occurs at points called chiasmata, where sections of chromatids are exchanged between homologous chromosomes.
• The nuclear envelope breaks down, and spindle fibres begin to form.

2. Metaphase I

• Bivalents align along the equator of the cell.
• Independent assortment occurs as the orientation of each homologous pair is random.

3. Anaphase I

• Homologous chromosomes are pulled apart to opposite poles of the cell by the spindle fibres.
• The chromatids remain attached at their centromeres.

4. Telophase I and Cytokinesis

• The cell divides into two haploid daughter cells, each containing one chromosome from each homologous pair.
• The nuclear membrane may reform briefly.

Meiosis II: Division of Chromatids

1. Prophase II

• Chromosomes condense again, and a new spindle apparatus forms.

2. Metaphase II

• Chromosomes align individually along the equator of the cell.
• Spindle fibres attach to the centromeres.

3. Anaphase II

• Sister chromatids are pulled apart to opposite poles as the centromeres divide.

4. Telophase II and Cytokinesis

• Nuclear envelopes reform around each set of chromosomes.
• The cytoplasm divides, resulting in four haploid daughter cells, each genetically distinct.