1. Meiosis Overview

4. Sexual Reproduction Defined: Gametes from two separate parents unite Meiosis: Diploid (2n) to haploid (n) cells Mechanism that allows for genetic diversity Many eukaryotes reproduce in this manner – Plants, animals and fungi

6. Meiosis: Prophase I Prophase I- chromosomes become visible and nuclear membrane breaks down. Crossing over occurs portions of one sister chromatid are broken and exchanged with portions of the corresponding chromatid of homologous chromosome.

7. Meiosis: Metaphase I Homologous chromosomes move to the middle of the cell and stay together.

8. Meiosis: Anaphase I The homologous chromosomes are pulled apart to opposite sides of the cell via spindle fibers. Notice that the sister chromatids are still linked together at the centromere.

9. Meiosis: Telophase I/ Cytokinesis A nuclear membrane reforms around the separated chromosomes Two new __________ diploid cells are formed

10. Meiosis II: Prophase II The nuclear membrane dissolves around the chromosomes

11. Meiosis II: Metaphase II Chromosomes line up in the middle of the cell and spindle fibers attach to sister chromatids’ centromeres

12. Meiosis II: Anaphase II The sister chromatids are pulled to opposite sides of the pole by the spindle fibers.

13. Meiosis II: Telophase II The nuclear envelope forms around each set of chromosomes Four unique haploid (1n) cells are formed

14. Genetic Variation Created ____________ ____________: the random distribution of homologous chromosomes Each of the 23 pairs of chromosomes separate independently of each other Thus, 2 23 (over 8 million) gametes can be produced by a single cell Gamete formation endless possibilities 2 23 x 2 23 = over 64 trillion unique zygotes Extremely important to the evolution of all species.

15. Meiosis Males Spermatogenesis: sperm production Females Oogenesis: egg (ova) production

16. Fertilization Gametes of opposite sexes join to make a diploid (2n) zygote Zygote: cell resulting from the fusion of gametes