CELL DIVISION mitosis & meiosis

1. CELL DIVISION mitosis & meiosis

2. Forms of DNA • When the cell is NOT dividing = chromatin • When the cell IS dividing = chromosome Monovalent chromosome Bivalent chromosome

3. Why do cells divide? • Replacement - cells wear out & die • Repair - tissues can be damaged by injury or infection • Growth of the organism • Reproduction

4. Types of cell division • Mitosis • New cells are identical to the old cells • Chromosome number is the same in parent & daughter cells (diploid -2n) • Growth, repair, & asexual reproduction

5. MITOSIS

6. Meiosis • Parent cell divides twice to produce 4 cells • Produces gametes (sex cells –sperm/eggs) • Daughter cells have half the original number of chromosomes (haploid -1n)

7. 4.When two gametes join to form a zygote, it will have the normal # of chromosomes

9. MEIOSIS

10. 5. Daughter cells are not Genetically identical • a.) Homologous chromosomes separate, sending one version of each to the new cells. • b.) Crossing –Over: sometimes chromosomal segements are exchanged between Homologous Chromosomes.

12. Phases of Mitosis • Interphase • Growth & normal cell activities • DNA = chromatin *as the cell prepares for division, DNA is duplicated

13. Prophase • Chromatin thickens & reveals duplicated chromosomes (bivalent) • Centrioles move to poles • Nuclear membrane dissolves

14. Metaphase • Bivalent chromosomes line up along equator of cell • Chromosomes attach to spindle fibers

15. Anaphase • Spindle fibers pull monovalent chromosomes to opposite ends of cell **an identical set of chromosomes moves to each pole

16. Telophase • Chromosomes uncoil & become chromatin again – Nuc. Memb Reforms • Cytokinesis: cell membrane pinches in to form 2 separate cells

17. Phases of Meiosis • Cells go through two rounds of division during meiosis, resulting in 4 haploid cells

18. Meiosis I & II Section 11-4 Diff. genes Same genes