1. Protein Synthesis Test – Tomorrow!

2. Meiosis

3. Similarities and Differences between Mitosis and Meiosis MitosisMeiosis Where does it occur in body? # Cell divisions # DNA replications Creates what type of cell? # Chromosomes in End product # Cells produced Function

4. Mitosis Review IPMAT Remember: Mitosis = Two Cells “Tea for Two”

5. Reasons for Mitosis Production of 2 daughter cells that are genetically identical Provides: – a) a means of asexual reproduction for unicellular organisms – b) replacement of worn out and damaged cells – c) growth of an organism

6. From Zygote to Embryo Zygote 2n Zygote 2n

8. Cleavage

11. Blastula From Zygote to Embryo

12. Meiosis Special type of cell division that produces haploid (n) sex cells (gametes) Meiosis is divided into 2 stages: Meiosis I and Meiosis II Consists of 1 replication and 2 divisions

13. Formation of gametes 46 23 How many chromosomes will baby have?

14. Germ Cells Male – Sperm producing machines – Germ cells are found in the lining of the seminiferous tubules (250m in each testicle) – Once they reach maturity, they constantly divide (Spermatogenesis) Female – Germ cells - found in follicles in ovaries and produced before birth – Cells are suspended in Prophase I and don’t continue to divide until puberty – Complete their division after being simulated by hormones during the menstrual cycle (Oogenesis)

15. MaleFemale

16. Similarities and Differences between Mitosis and Meiosis MitosisMeiosis Where does it occur in body? # Cell divisions # DNA replications Creates what type of cell? # Chromosomes in End product # Cells produced Function

17. Let’s carry out an example for a mosquito cell Diploid Number (2n) = 6

18. Period of growth of germ cells DNA replicates Interphase I Early Interphase I Late Interphase I

19. Prophase I Nuclear envelope disappears Replicated chromatin coils into chromatid pairs Centrioles move to opposite poles of the cell and start producing protein fibers that form the spindle

20. Prophase I Synapsis – Chromatid pairs attach to form tetrads Crossing over – During synapsis, arms of chromatid pairs exchange segments of DNA at chiasma – Increases genetic diversity

21. Prophase I Early Prophase ILate Prophase I

22. Meiosis I – Metaphase I Tetrads line up at the equator of spindles

23. Meiosis I – Anaphase I Tetrads separate in an event called disjunction Chromatid pairs are pulled to poles of cell Cleavage furrow begins to form

24. Meiosis I – Telophase I Cleavage furrow formation is complete and cytokinesis occurs Nuclear envelope reappears

28. Meiosis II – Prophase II Most cells skip Interphase II and proceed right into Prophase II Meiosis II follows the stages of Mitosis

29. Meiosis II – Metaphase II

30. Meiosis II – Anaphase II

31. Meiosis II – Telophase II

32. Differences of Meiosis and Mitosis Synapsis – Happens in Prophase I – Tetrad formation Crossing over – Happens in Prophase I – Arms of chromatids in a tetrad swap DNA – Increases genetic diversity Disjunction – Happens in Anaphase I – Tetrads separate and chromatid pairs are pulled to opposite sides of the cell Non-Disjunction – Happens in Anaphase I – A tetrad does not separate and sex cells are formed with abnormal chromosome numbers

33. Meiosis Square Dance

35. Step by Step Meiosis Animation

36. Dry Lab

37. In which phases will these terms be present? Chromatin Replicated Chromatin Chromatid Pairs Tetrads Chromosomes

38. Draw the stages of Meiosis from Metaphase I to Telophase II if non- disjunction were to occur