1. Meiosis

2. Why Do cells Go through Meiosis?
Cells go through Meiosis in order to make Sex Cells
Sex cells are also called Gametes
Four Daughter Cells are created
Haploid (1N)

3. Interphase
Cell Grows
Duplicates DNA
Cell Prepares to divide

4. After Interphase
In order to make sex cells or cells with half the number of chromosomes meiosis has TWO phases
Meiosis I and Meiosis II

5. Prophase I Chromosomes Condense (visible)
Homologous chromosomes form a tetrad (4 chromatids)- paring up called SYNAPSIS
Crossing Over Occurs

6. Crossing Over
Homologous Chromosomes- Similar chromosomes and genes in the same location, but come from different parents
When the chromosomes touch they switch genetic information CROSSOVER
Causes genetic variation in the resulting gametes

7. Knowledge Check Why do cells go through meiosis?
A- to replicate body cells B- To replicate sex cells
What’s the name of the type of cell formed through meiosis?
A- gametes B- somatic cells
What important event leads to genetic variation?
A- homologous chromosomes B- Tetrad
C-Crossover

8. Crossover close-up with results

9. Metaphase I
Homologous chromosomes move together to the middle of the cell
Spindle attaches to the centromere

10. Anaphase I Homologous chromosomes separate
Sister chromatids stay attached
Move towards opposite poles

11. Telophase I Division of cytoplasm Creates Two daughter cells
Begin Meiosis II
There is a brief interphase, but no DNA replication
Why?

12. Knowledge Check During Anaphase I in meiosis:
A- The sister chromatids separate to opposite poles
B- The homologous chromosomes separate to opposite poles
Name the stage

13. Prophase II
Spindles re-appear
Nuclear membrane stays separated

14. Metaphase II Chromosomes line up in the middle Spindle attaches
How are metaphase I and II different?

15. Anaphase II Sister Chromatids Separate from each other
How are Anaphase I and II different from eachother?

16. Telophase II Nucleus reforms Division into four daughter cells
Haploid (1N)
Gametes (egg and sperm)

17. Knowledge Check- Name the phase

18. Final Results of Meiosis
4 haploid daughter cells which will develop into sex cells
Each daughter cell has half of the genetic information of a somatic cell
23 chromosomes for each sex cell
NOTE:
Males will create 4 sperm cells for every one cell that goes through meiosis
Females will create 4 egg cells, BUT 3 will turn into non usable polar bodies and 1 will mature into an egg cell.

21. Let’s watch Meiosis in Motion

22. Through sexual reproduction and fertilization, these gametes fuse to form one diploid cell again (2n 46 chromosomes).

23. Zygote= a fertilized egg
Zygote will begin to rapidly mitotically divide to make more cells to form a BLASTOCYST and then develop into an EMBRYO.

24. Fertilization and Life

25. Clay meiosis
As a class we will use the clay, yarn, and string to go through the phases of meiosis so that you can visually see what happens

26. Create Prophase 1 with your clay and yarn- SHOW CROSSOVER

27. Create metaphase 1 with your clay and yarn

28. Create anaphase 1 with your clay and yarn

29. Create Telophase 1 with your yarn and clay

30. Move the chromosomes in position for prophase and metaphase 2- NOTICE EACH CHROMOSOME IS DIFFERENT

31. Position the chromosomes, spindle fibers, and centrioles to anaphase II

32. Position your chromosomes for telophase and cytokinesis

33. Things to notice about the results
4 resulting daughter cells. Contains only 1 set of genetic information in the chromosome haploidn
Each daughter cell is contains chromosomes that are genetically different from one another
These daughter cells will develop into full sex cells (gametes). Sperm for males and egg for female