Meiosis is the process of cell division that produces gametes, such as sperm and egg cells, required for sexual reproduction. It reduces the number of chromosomes in each cell from the diploid number of 46 to the haploid number of 23. This occurs through two cell division phases, Meiosis I and Meiosis II, resulting in four haploid daughter cells from one original diploid parent cell. Meiosis occurs specifically in the gonads or sex organs to produce either sperm or egg cells, allowing for genetic material from two parents to combine via fertilization to form a zygote with the full chromosome number.

1. Meiosis
Grade 9 - RE 9.2
Ms. Zahid

2. Meiosis
Cell division in gametes
Required for sexual reproduction
Produces half the number of chromosomes (n)
diploid (2n) ———> haploid (n)
Two divisions (Meiosis I and Meiosis II)

3. Why do we need
Meiosis?
We need half of our DNA from each parent!
Gametes from each parent (sperm and egg)
form a zygote - a fertilized egg.
FERTILIZATION!

4. Where does Meiosis
occur?
Occurs only in gonads (testes or ovaries)
Male: spermatogenesis
Female: oogenesis

5. Spermatogenesis

6. Let’s take a look under the microscope!

7. Oogenesis

8. Interphase
Chromosomes have now replicated and similar to
Mitosis are ready for cell division.
Each duplicated chromosome has 2 identical
sister chromatids attached at the centromere.
Have 4 centrioles in pairs of two.

9. Interphase
Nucleus and nucleolus are visible

10. Meiosis I
Have 4 Phases:
Prophase I
Metaphase I
Anaphase I
Telophase I
At the end of Meiosis I, we will have half the number of
chromosomes.

11. Prophase I
Longest phase of Meiosis I
Chromosomes condense
Homologous chromosomes come to form a tetrad, in
a process called Synapsis.
Tetrad is two chromosomes or four chromatids.

12. Prophase I

13. Metaphase I
Shortest phase
Tetrads align on the metaphase plate.
Independent assortment occurs:
Orientation of the homologous pairs is
random

14. Metaphase I

15. Anaphase I
Homologous chromosomes separate and move
towards the opposite poles.
Sister chromatids remain attached at their
centromeres.

16. Anaphase I

17. Telophase I and
Cytokinesis
Each pole now has haploid set of chromosomes.
Cleavage furrow forms. Cells begin to divide into two daughter cells.
Cell completely divides and two haploid daughter cells are formed.

18. Meiosis II

19. Prophase II
Similar as prophase in mitosis
What do you notice here?

20. Metaphase II
Same as metaphase in mitosis
Sister chromatids line up on the metaphase
plate.

21. Anaphase II
Same as anaphase in Mitosis
Sister chromatids separate

22. Telophase II
Nuclei form
Same as Telophase in Mitosis
But remember, four haploid daughter cells are
produced.

23. Telophase II

24. Meiosis Overall

25. Fertilization
What happens to the cells that went through
meiosis?
The fusion of a sperm and egg is what forms a
zygote.
This is now considered a fertilized egg.

26. Review Questions
What is a haploid cell?
Why does Meiosis have haploid cells?
In which cells does Meiosis occur?
Is Meiosis similar to Mitosis?
Is it more similar to Meiosis I or II?

27. See you next class!