Meiosis Click and Learn! Explore each stage in more detail! [link]

Stage Description
Prophase I

1.     Homologous chromosomes (matching chromosomes from mother and father) pair up.

2.     Crossing over occurs in this stage.

3.     Spindle fibres form

4.     Nuclear Membrane breaks down
Metaphase I 1.     Homologous pairs line up along the equator of the cell

Anaphase I

 

 

1. Homologous chromosomes separate and are pulled to opposite poles by the spindle fibres.

 

Telophase I

 

 

 1.     One chromosome from each homologous pair is at each pole of the cell.
Prophase II

1.     There is one chromosome of the homologous pair in each cell.

 
Metaphase II

1.     The X-shaped chromosomes form a single line across the middle of the cell.

 
Anaphase II

1.     Sister chromatids move to opposite pols of the cell. Once they separate, each sister chromatid is considered to be a chromosome.

 
Telophase II

1.     Spindle fibres begin to disappear, and a nuclear membrane forms around each set of chromosomes.

 

 

Characteristics unique to meiosis:

  • Pairing of homologous chromosomes – Meiosis I differs from mitosis because in meiosis I a pair of matching chromosomes, one from each parent, lines up at the equator. This happens in metaphase In mitosis chromosomes line up alone.
  • Crossing Over – Occurs during meiosis I. Non-sister chromatids “cross over” and exchange pieces of DNA with each other. This creates more diversity in chromosomes since they have changed pieces with another.
  • Independent Assortment – Chromosomes sort themselves independently of other pairs. That means each chromosome pair has 2 possible arrangements (Chromosome from father on right, Mother on left OR chromosome from father on left, mother on right). Times this by 23 chromosomes and we get over 8 million possibilities!