Meiosis

1
Meiosis

• Division of Sex Cells

2
Meiosis

• A process of reduction division in which the
  number of chromosomes per cell is cut in half
  through the separation of homologous chromosomes
  in a diploid cell.
• Diploid 2 sets of chromosomes
• Haploid 1 set of chromosomes
• Homologous chromosomes that each have a
  corresponding chromosome from the opposite sex
  parent

3
Meiosis
4
Meiosis Stages

• Meiosis usually involves 2 distinct stages
• Meiosis I
• Meiosis II

5
Prophase I

• Each chromosome pairs with its corresponding
  homologous chromosome to form a tetrad.
• There are 4 chromosomes in a tetrad.
• The pairing of homologous chromosomes is the key
  to understanding meiosis.
• Crossing-over may occur here
• Crossing-over is when chromosomes overlap and
  exchange portions of their chromatids.

6
Prophase I
7
Metaphase I

• Spindle fibers attach to the chromosomes

8
Metaphase I
9
Anaphase I

• The fibers pull the homologous chromosomes toward
  opposite ends of the cell.

10
Anaphase I
11
Telophase I Cytokinesis

• Nuclear membranes form.
• The cell separates into 2 cells.

12
Telophase I
13
Prophase II

• Meiosis I results in two haploid (N) cells.
• Each cell has half the number of chromosomes as
  the original cell.

14
Prophase II
15
Metaphase II

• The chromosomes line up similar to metaphase in
  mitosis.

16
Metaphase II
17
Anaphase II

• Sister chromatids separate and move to opposite
  ends of the cell.

18
Anaphase II
19
Telophase II

• Meiosis II results in 4 haploid cells.

20
Telophase II
21
Gamete Formation

• In males, meiosis results in 4 sperm cells
• In females, meiosis results in 1 egg cell and
  three polar bodies, which are not used in
  reproduction.

22
Mitosis vs Meiosis
Mitosis Meiosis
Results in 2 Diploid Cells (2N) 4 Haploid Cells (N)
Cells are Genetically Identical Genetically Different
Occurs in Somatic (Body) Cells Sex Cells