1. Meiosis and Fertilization my-OH-sis

2. Meiosis is cell division used for: Producing gametes (sex cells) What is Meiosis? ***Makes 4 different cells!***

3. Part of it looks like mitosis! Meiosis

4. DNA replicates once, cell divides twice Creates haploid (n) sex cells In humans, takes place in ovaries and testes Meiosis

5. Prophase 1 Chromosomes become visible and the nuclear membrane breaks apart Crossing over occurs! Creates new gene combinations!

6. Metaphase 1 vs. 2 Metaphase 1- homologous chromosomes pair up in the middle Metaphase 2- single chromosomes line up in the middle

7. Anaphase 1 vs. 2 Anaphase 1- homologous chromosomes separate and move apart Anaphase 2- Chromatids separate and move apart

8. Telophase 1 vs. 2 Telophase 1- Single cell splits into 2 cells, goes right into Prophase 2 Telophase 2- Two cells each split, creating 4 haploid cells

9. Meiosis: A Second Look

10. Meiosis results in 4 genetically different haploid daughter cells One major point! *These cells are sperm and eggs!

11. Fertilization n n + = 2n Haploid Egg cell 23 chromosomes Haploid Sperm cell 23 chromosomes Diploid Zygote 46 chromosomes

13. Homework Review 1.Describe the main results of meiosis. 2.What are the principal differences between mitosis and meiosis? 3.What do the terms diploid and haploid mean? 4.What is crossing-over? 5.In human cells, 2N=46. How many chromosomes would you expect to find in a sperm cell? In an egg cell? In a white blood cell? Explain.