1. Meiosis: The Process
Biology 12

2. Cartoon of the day:

3. Context:
Meiosis allows
for the formation
of sperm and
egg cells

4. Overview: Interphase Meiosis I Meiosis II Prophase I Metaphase I
Anaphase I
Telophase I (and cytokinesis)
Meiosis II
Prophase II
Metaphase II
Anaphase II
Telophase II (and cytokinesis)

5. Meiosis I: Interphase
The chromatin begins to condense into chromosomes, which duplicate
Identical to interphase in mitosis
Chromosome duplication

6. Meiosis I: Prophase I
In meiosis (unlike mitosis), the process called synapsis occurs.
Tetrads of homologous chromosome form
There may be an exchange of genetic material, called crossing over

7. Crossing over (synapsis):
Non-sister chromatids of homologous chromosomes interchange genes
The pairing (formation of the tetrad) allows crossing over to take place and this enables genetic variations in the daughter cells.

8. Meiosis I: Metaphase I Tetrads line up at the equator
Alignment is random so that chromosomes from one parent will be mixed with the other parent when they move apart

9. Meiosis I: Anaphase I
One homologous chromosome of each pair is pulled to each end of the cell.
**Remember in mitosis, it was the chromatids that separated, not pairs of chromosomes!

10. Meiosis I: Telophase I (and cytokinesis I)
The cell begins to divide into two daughter cells.
Each cell produced after cytokinesis has been reduced from diploid to haploid.

11. Interphase:
Very short
DNA is not replicated before meiosis II

12. Meiosis II: Prophase II
Nuclear membrane begins to dissolve
Spindle fibers begin to form

13. Meiosis II: Metaphase II
Spindle fibres attach to centromeres
Sister chromatids line up at equator

14. Meiosis II: Anaphase II
Centromeres divide in two
Spindle fibres pull sister chromatids towards opposite ends of cell (pole)

15. Meiosis II: Telophase II and (cytokinesis II)
Nuclear membrane reforms and cytoplasm divides

16. Result: Formation of four cells Are sex cells (egg or sperm)
Haploid (carries half the number of chromosomes of somatic cells)

17. Videos: http://www.youtube.com/watch?v=kVMb4Js99tA

18. To do: Meiosis colouring sheet Read pages 103-107