1. Meiosis & Sexual Reproduction
Ag Biology

2. A form cell division that halves the number of chromosomes when forming reproductive cells (gametes)
What is Meiosis?

3. Involves 2 divisions of the nucleus:
Meiosis I
Meiosis II
46 Chromosomes
92 Chromosomes
46 Chromosomes
Meiosis I
Meiosis II
23 Chromosomes

4. Before meiosis begins, the DNA in the original cell is copied.
Step 1: Prophase I
Chromosomes condense
Nuclear envelope breaks down
Cross-over occurs
Steps in Meiosis

5. Crossover occurs when portions of a chromatid are broken and exchanged with the corresponding portion of the second chromatid.
What is Cross-over?

6. Step 2: Metaphase I Step 3: Anaphase I
Pairs of homologous chromosomes move to the equator of the cell
Step 3: Anaphase I
Pairs of homologous chromosomes move to the opposite poles of the cell

7. Step 4: Telophase I & Cytokinesis
Chromosomes gather at the poles of the cell
Cytoplasm divides
Step 5: Prophase II
New spindle forms around the chromosomes.

8. Step 6: Metaphase II Step 7: Anaphase II
Chromosomes line up at the equator
Step 7: Anaphase II
Chromosomes divide and move to opposite poles of the cell.

9. Step 8: Telophase II & Cytokinesis
Nuclear envelope forms around each set of chromosomes
Cytoplasm divides

10. Meiosis Drawing Fold a sheet of paper into 8 sections
Using colored pencils, draw a cell as it goes through each of the 8 stages of meiosis
Label each stage
Briefly explain what occurs in each stage
Make sure to put your name, date, period on it
Turn in by the end of the period
Meiosis Drawing

11. Gametogenesis Formation of gametes (sperm & eggs) In females oogenesis
In males spermatogenesis
Gametogenesis

12. Oogenesis Process by which the eggs are produced in females
Occurs in the ovaries
In cytokinesis following meiosis I, the cytoplasm divided unequally
One cell gets nearly all the cytoplasm which will become the egg cell
Cell must contain nutrients to nourish the young organism if the egg is fertilized
Other cells are small and are called polar body.
Polar bodies die
Oogenesis

13. Oogenesis

14. Spermatogenesis Process by which sperm are produced in males
Occurs in the testes
4 haploid cells are produced
These cells change in form and develop a tail to become sperm
Spermatogenesis