In-depth Notes on Meiosis Phases

Cell Division: Meiosis Overview

• Meiosis is a specialized type of cell division that reduces the chromosome number by half, resulting in gametes (sperm and egg cells).

Phases of Meiosis

Meiosis I

1. Prophase I

   • The nuclear membrane breaks down.
   • Chromosomes condense and become visible.
   • Paired homologous chromosomes (homologous pairs) align and pair up, exchanging genetic material through crossing-over.
   • Spindle fibers begin to form.

2. Metaphase I

   • Homologous chromosome pairs line up along the equatorial plane of the cell.
   • Spindle fibers attach to each homologous chromosome.

3. Anaphase I

   • The paired homologous chromosomes are pulled apart by the spindle fibers.
   • Homologous chromosomes move towards opposite ends of the cell.

4. Telophase I

   • The cell begins to divide: cytokinesis occurs, resulting in two new cells.
   • New nuclear membranes form around each set of chromosomes.
   • Each new cell now contains one duplicated chromosome from each pair.

Meiosis II

1. Prophase II

   • Chromosomes, each consisting of two sister chromatids, condense again.
   • The nuclear membrane breaks down if it was reformed in the previous phase.
   • Spindle fibers reassemble.

2. Metaphase II

   • Chromosomes line up at the center of the cell.
   • Spindle fibers attach to sister chromatids.

3. Anaphase II

   • Sister chromatids are separated and pulled towards opposite poles of the cell by the spindle fibers.

4. Telophase II

   • New nuclear membranes form around each set of chromosomes.
   • Cytokinesis occurs, resulting in four genetically diverse haploid cells.
   • Each cell contains one copy of half the genetic information from the original cell.

Summary of Key Points

• Each Meiosis results in four non-identical haploid gametes.
• Processes like crossing-over contribute to genetic diversity among offspring.
• Understanding the sequence of meiosis is vital for comprehending genetic inheritance and variation.