2. MEIOSIS NOTES Double cell division

3. Reproduction Asexual (relies on mitosis): used to create new identical organisms. All of the parent organism’s DNA goes to the new cells.  For example: in humans; the new cells have 46 chromosomes Sexual (relies on meiosis): used to create sex cells. In humans, each sex cell contains 23 chromosomes.

4. 2 TYPES OF CELLS 1) BODY CELLS – somatic cells 2) SEX CELLS - gametes

5. Types of Cells 1) Body Cell - all cells other than sex cells - Also called somatic cells -Made by mitosis -These cells are a identical to their “parent” This is a red blood cell

6. Types of Cells: Body Cells - Somatic (body) cells contain 2 copies of each chromosome - these chromosomes are called homologous (the same) chromosomes -they have diploid # 2p EX. Humans =46

7. Types of Cells: 2) Sex Cells - Also called gametes - Eggs and sperm cells - Made by meiosis - Have haploid # p *EX. Humans =23

8. Sex Cells (sea urchin egg being fertilized by sperm cells from another sea urchin)

9. When sexual reproduction occurs: Egg (haploid #)Sperm (haploid #) ZYGOTE (diploid #) Ex. Humans 23 + 23 =46

10. Meiosis The Reduction division - starts with 1 diploid (2p) cell. It goes through meiosis 1 (similar to mitosis), then through meiosis 2, and ends up with 4 haploid (p) cells

11. Meiosis occurs in 2 steps Step = MEIOSIS I Step = MEIOSIS II

12. MEIOSIS I Meiosis I = (I1, P1, M1, A1, T1. C1) -homologous chromosome pairs are divided -two new daughter cells are produced with identical DNA.

13. MEIOSIS 2 Meiosis II (I2, P2, M2, A2, T2, C2) -Two sister chromatids are split into two daughter cells -Meiosis is different from mitosis because in mitosis the chromosome # stays the same, but in meiosis the number of chromosomes is cut in half.

14. Meiosis Diagram

15. CROSSING OVER - “Crossing over” occurs during the first Prophase of meiosis - In “crossing over” Tetrads form and DNA is exchanged XXXX - ADVANTAGE: genetic variation- we don’t all look or act the same!!!!

16. Crossing Over Adapted from: Morgan T.H., Sturtevant A.H., Muller H.J., and Bridges C.B., "The Mechansim of Mendelian Heredity", 1915.

17. Gamete Development in Males and Females MALES Meiosis occurs in testes at puberty and then occurs as needed. All four sperm cells survive. This process in men happens every 24 hours. Men are constantly producing new sperm cells. FEMALES Meiosis occurs in the ovaries before birth. You are born with all of your eggs. Three out of the four eggs produced by meiosis dies because it is small and cannot sustain itself.

18. Comparing Mitosis and Meiosis HOW MANY CELLS ARE MADE? In mitosis= In meiosis=

19. Comparing Mitosis and Meiosis ARE RESULTING CELLS GENETICALLY THE SAME OR DIFFERENT? In mitosis? Genetically the same In meiosis? Genetically different

20. Comparing Mitosis and Meiosis WHAT TYPES OF CELLS RESULT IN THE PROCESS? (SOMATIC CELLS OR GAMETES) In mitosis? Identical somatic (body) cells In meiosis? Gametes (sex cells)

21. Comparing Mitosis and Meiosis WHAT IS THE PURPOSE OF EACH PROCESS? In mitosis? Growth, repair, or replacement In meiosis? Formation of sex cells and genetic variation