1. Meiosis

2. Meiosis involves 2 parents (usually)
hereditary material is exchanged (mixed and transferred)
Each species has a specific number of chromosomes
For example humans total number of chromosomes is 46
diploid number is 46 or 2n = 46
the number of chromosomes in the gametes is the haploid number or n = 23
Other examples: crayfish 2n = 126 fruit flies 2n = 4

3. Meiosis Meiosis animation (1:49 min):
Beginning of third class

4. Vocabulary Diploid Haploid Germ cell (Gamete) Somatic cell Interphase
Prophase
Metaphase
Anaphase
Telophase
Cytokinesis

5. Each resulting cell still has chromosomes from mom & dad

6. Interphase Meiosis is preceded by interphase
chromosomes have not yet condensed

7. Interphase
chromosomes have replicated, and the chromatin begins to condense

8. Meiosis Prophase I the chromatin shortens to form chromosomes
homologous chromosomes pair up or synapse to form tetrads

9. Synapsis in Prophase I of Meiosis

10. Meiosis Metaphase I
chromosomes line up across the middle, or equator, of the cell
centromeres of chromosomes attach to spindle fibres

11. Meiosis Anaphase I
homologous chromosomes separate and move along spindle fibres towards the poles or ends of the cell

12. Meiosis Telophase I & Cytokinesis
cell begins to divide into two daughter cells
each daughter cell can get any combination of maternal and paternal chromosomes
cell has divided into two daughter cells

13. Meiosis Prophase II
nuclear membrane dissolves and the spindle fibres begin to form

14. Meiosis Metaphase II
as in Meiosis I, the chromosomes line up on the spindle fibers
sister chromatids remain attached at their centromeres

15. Meiosis Anaphase II
centromeres split and sister chromatids separate and move to opposite poles of the cell
chromatids are now called chromosomes

16. Telophase II & Cytokinesis
With the formation of four cells, meiosis is over.
Each of these prospective germ cells carries half the number of chromosomes of somatic cells.

17. Comparing Mitosis and Meiosis

18. Comparing Chromosome Numbers in Mitosis and Meiosis