1. More On Cell Division

2. What if you got paid… Just 1 sen per week. Just 1 sen per week. Every week your pay doubles. Every week your pay doubles. How much would you be paid the 4 th week? How much would you be paid the 4 th week? 1 sen, 2 sen, 4 sen, 8 sen… 1 sen, 2 sen, 4 sen, 8 sen… How much would you be paid the 10 th week? How much would you be paid the 10 th week? 1, 2, 4, 8, 16, 32, 64, RM 1.28, 2.56, 5.12 1, 2, 4, 8, 16, 32, 64, RM 1.28, 2.56, 5.12 How much would you be paid the 16 th week? How much would you be paid the 16 th week? RM10.24, 20.48, 40.86, 81.72, 163.44, 326.88 RM10.24, 20.48, 40.86, 81.72, 163.44, 326.88 Geometric Progression

3. Fertilization Zygote Gametes SpermOvum

4. In sexual reproduction, reproductive cells combine— In sexual reproduction, reproductive cells combine— female — ovum, male — sperm What would happen if the reproductive cells each had the same number of chromosomes as the parent’s body cells? What would happen if the reproductive cells each had the same number of chromosomes as the parent’s body cells? This Leads To A Question What happens so that living things avoid having too many chromosomes from sexual reproduction?

5. As we begin… Let’s review the stages of cell division as we already know them… Let’s review the stages of cell division as we already know them… Interphase Interphase Prophase Prophase Metaphase Metaphase Anaphase Anaphase Telophase Telophase These are the stages of… These are the stages of…

6. Mitosis Video 1 Video 2

7. A B C DE F A B C D E F

8. A B C DE F A B C DE F

9. What happens so that living things avoid having too many chromosomes from sexual reproduction? ? Somatic Cell 2n=23 pairs=diploid kary

10. What happens so that living things avoid having too many chromosomes from sexual reproduction? Mitosis ? Somatic Cell 2n=23 pairs=diploid Normal Somatic Cells 2n=23 pairs=diploid

11. A Different Kind of Cell Division Meiosis ? Somatic Cell 2n=23 pairs of chromosomes diploid Reproductive Cells n=23 chromosomes haploid (gametes)

12. Fertilization Zygote (diploid) Gametes SpermOvum (haploid)

13. A Different Kind of Cell Division Meiosis 2 Cycles Meiosis I Interphase I Prophase I Metaphase I Anaphase I Telophase I Meiosis II Prophase II Metaphase II Anaphase II Telophase II

14. Meiosis I Interphase Mother cell Meiosis II Prophase I: Tetrad formation Prophase I: Tetrad formation Metaphase I Prophase I: Condensing Chromosomes Prophase I: Condensing Chromosomes Anaphase I Telophase I Note Centromeres Note bivalents of homologous Chromosomes

15. Telophase I Meiosis II Meiosis II Metaphase II Anaphase II Telophase II Prophase II Note that before Prophase II There is no replication of DNA

16. Prophase I: Tetrad formation/ crossing over Prophase I: Tetrad formation/ crossing over Anaphase I Metaphase I Telophase I Because of crossing over, every gamete receives a unique set of genetic information. Crossing Over Crossing Over Site of crossover is called chiasma

17. What is each diagram showing?

18. What is shown?

19. Mitosis--Interphase

20. Meiotic Interphase Growth 1 (G1) phase: Immediately follows cytokinesis. Immediately follows cytokinesis. Very active period, Very active period, Synthesis of proteins Synthesis of proteins each of the 46 human chromosomes consists of a single (very long) molecule of DNA. each of the 46 human chromosomes consists of a single (very long) molecule of DNA. At this point cells are 46,2N, identical to somatic cells. At this point cells are 46,2N, identical to somatic cells. Synthesis (S) phase: genetic material is replicated: genetic material is replicated: each of its chromosomes duplicates (46,2N). each of its chromosomes duplicates (46,2N). cell is still diploid, however, because it still contains the same number of centromeres. cell is still diploid, however, because it still contains the same number of centromeres. chromatids are in the chromatin form because spiralisation and condensation into denser chromosomes have not taken place yet. chromatids are in the chromatin form because spiralisation and condensation into denser chromosomes have not taken place yet. Growth 2 (G2) phase: G2 phase is absent in Meiosis

21. How could you explain… Remember our question: Remember our question: What happens so that living things avoid having too many chromosomes from sexual reproduction? Write a short explanation as you would for someone who does NOT know about meiosis. Write a short explanation as you would for someone who does NOT know about meiosis. Avoid science vocabulary for now. Use 5-10 sentences—try to be brief.