1. Division to produce Sex Cells
Meiosis
Division to produce Sex Cells

2. Meiosis-
A process of cell division in which a diploid cell produces haploid gametes by separating homologous pairs of chromosomes.
Diploid – 2 sets of chromosomes
Haploid – 1 set of chromosomes
Gamete – sex cells, (sperm, egg, pollen, ovum)
Homologous – pairs of matching chromosomes that come from each parent (numbered 1-23 in humans)

4. Meiosis

5. Meiosis Stages Meiosis involves 2 distinct cell divisions: Meiosis I
(P,M,A,T)
Meiosis II
Meiosis Animation

6. Prophase I
Each chromosome pairs with its corresponding homologous chromosome to form a tetrad.
There are 4 chromosomes in a tetrad (2 pairs of sister chromatids)
The pairing of homologous chromosomes is the key to meiosis.
Crossing-over may occur here
Crossing-over is when chromosomes
overlap and exchange portions of their
DNA (genes)
“CROSSING OVER” is like “shuffling the
genetic deck”- called RECOMBINATION

7. Prophase I

8. Metaphase I Homologous pairs line up side by side in middle of cell
It is RANDOM which side the maternal and paternal chromosomes line up on
“RANDOM ASSORTMENT” is a second “shuffling of the genetic deck”

9. Anaphase I
Homologous pairs pulled apart. (Not sister chromatids!!)

10. Telophase I & Cytokinesis
Nuclear membranes form.
The cell separates into 2 HAPLOID cells.

11. End of Meiosis I Meiosis II
Meiosis I results in two haploid (1N) cells.
Each cell has half the number of chromosomes as the original cell.
Meiosis II
Starts immediately after Meiosis I (no interphase)
Meiosis II is basically just like Mitosis

12. Prophase II
Chromosomes re-condense and nuclear membrane breaks down again (similar to Prophase of Mitosis)

13. Metaphase II
The chromosomes line up similar to metaphase in mitosis.

14. Anaphase II
Sister chromatids separate and move to opposite sides.

15. Telophase II and Cytokinesis
Meiosis II results in 4 GENETICALLY DIFFERENT haploid cells. (gametes)

16. Gamete Formation
In males, meiosis results in 4 sperm cells (spermatogenesis)

17. Gamete Formation
In females, meiosis results in 1 egg cell and three polar bodies, which are not used in reproduction. (Oogenesis)

18. 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