1. Meiosis

2. Purpose of Meiosis To make gametes for sexual reproduction –To create diversity

3. What are gametes? –Gametes are “sex cells.” Sperm in males Ova (eggs) in females. –Each gamete is haploid (contains only one copy of each chromosome instead of two). –Every gamete is completely unique.

4. Starting point Only special cells can go through meiosis. –Spermatogonia –Oogonia

5. Where does meiosis occur? In males, sperm are made in the testes. In females, ova (eggs) are made in the ovaries.

6. Stages of Meiosis

7. Interphase The stage between divisions Consists of three steps: –G1 – Cell growth –S – copying the chromosomes –G2 – preparing to divide

8. Prophase 1 Chromosomes condense Nuclear envelope begins to dissolve Nucleolus disappears Tetrads form and crossing over occurs

9. Crossing Over The process in which homologous chromosomes trade parts.

10. Homologous Chromosomes Matching chromosomes. One from mom; one from dad.

11. Metaphase 1 Homologous chromosomes line up in the middle

12. Anaphase 1 Homologous chromosomes are pulled apart.

13. Telophase 1 Two new nuclei form

14. Prophase 2 Nuclear envelopes break down again

15. Metaphase 2 Chromosomes line up in the middle

16. Anaphase 2 Sister chromatids are pulled apart

17. Telophase 2 4 new nuclei are formed

18. Product of Meiosis Each spermatagonia makes 4 sperm. Each oogonia makes one ovum and 3 polar bodies.

19. Mendel’s Law of Segregation An individual’s alleles separate randomly during meiosis.